diff --git a/src/harness/unittests/compileOnSave.ts b/src/harness/unittests/compileOnSave.ts
index fde83170f36..24fd47ee0cb 100644
--- a/src/harness/unittests/compileOnSave.ts
+++ b/src/harness/unittests/compileOnSave.ts
@@ -3,6 +3,10 @@
 /// <reference path="../../server/typingsInstaller/typingsInstaller.ts" />
 
 namespace ts.projectSystem {
+    function createTestTypingsInstaller(host: server.ServerHost) {
+        return new TestTypingsInstaller("/a/data/", /*throttleLimit*/5, host);
+    }
+
     describe("CompileOnSave affected list", () => {
         function sendAffectedFileRequestAndCheckResult(session: server.Session, request: server.protocol.Request, expectedFileList: { projectFileName: string, files: FileOrFolder[] }[]) {
             const response: server.protocol.CompileOnSaveAffectedFileListSingleProject[] = session.executeCommand(request).response;
@@ -105,7 +109,7 @@ namespace ts.projectSystem {
 
             it("should contains only itself if a module file's shape didn't change, and all files referencing it if its shape changed", () => {
                 const host = createServerHost([moduleFile1, file1Consumer1, file1Consumer2, globalFile3, moduleFile2, configFile, libFile]);
-                const typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+                const typingsInstaller = createTestTypingsInstaller(host);
                 const session = new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
 
                 openFilesForSession([moduleFile1, file1Consumer1], session);
@@ -130,7 +134,7 @@ namespace ts.projectSystem {
 
             it("should be up-to-date with the reference map changes", () => {
                 const host = createServerHost([moduleFile1, file1Consumer1, file1Consumer2, globalFile3, moduleFile2, configFile, libFile]);
-                const typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+                const typingsInstaller = createTestTypingsInstaller(host);
                 const session = new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
 
                 openFilesForSession([moduleFile1, file1Consumer1], session);
@@ -177,7 +181,7 @@ namespace ts.projectSystem {
 
             it("should be up-to-date with changes made in non-open files", () => {
                 const host = createServerHost([moduleFile1, file1Consumer1, file1Consumer2, globalFile3, moduleFile2, configFile, libFile]);
-                const typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+                const typingsInstaller = createTestTypingsInstaller(host);
                 const session = new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
 
                 openFilesForSession([moduleFile1], session);
@@ -195,7 +199,7 @@ namespace ts.projectSystem {
 
             it("should be up-to-date with deleted files", () => {
                 const host = createServerHost([moduleFile1, file1Consumer1, file1Consumer2, globalFile3, moduleFile2, configFile, libFile]);
-                const typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+                const typingsInstaller = createTestTypingsInstaller(host);
                 const session = new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
 
                 openFilesForSession([moduleFile1], session);
@@ -210,7 +214,7 @@ namespace ts.projectSystem {
 
             it("should be up-to-date with newly created files", () => {
                 const host = createServerHost([moduleFile1, file1Consumer1, file1Consumer2, globalFile3, moduleFile2, configFile, libFile]);
-                const typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+                const typingsInstaller = createTestTypingsInstaller(host);
                 const session = new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
 
                 openFilesForSession([moduleFile1], session);
@@ -247,7 +251,7 @@ namespace ts.projectSystem {
                 };
 
                 const host = createServerHost([moduleFile1, file1Consumer1, configFile, libFile]);
-                const typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+                const typingsInstaller = createTestTypingsInstaller(host);
                 const session = new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
 
                 openFilesForSession([moduleFile1, file1Consumer1], session);
@@ -264,7 +268,7 @@ namespace ts.projectSystem {
 
             it("should return all files if a global file changed shape", () => {
                 const host = createServerHost([moduleFile1, file1Consumer1, file1Consumer2, globalFile3, moduleFile2, configFile, libFile]);
-                const typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+                const typingsInstaller = createTestTypingsInstaller(host);
                 const session = new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
 
                 openFilesForSession([globalFile3], session);
@@ -290,7 +294,7 @@ namespace ts.projectSystem {
                 };
 
                 const host = createServerHost([moduleFile1, file1Consumer1, file1Consumer2, configFile, libFile]);
-                const typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+                const typingsInstaller = createTestTypingsInstaller(host);
                 const session = new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
                 openFilesForSession([moduleFile1], session);
                 sendAffectedFileRequestAndCheckResult(session, moduleFile1FileListRequest, []);
@@ -308,7 +312,7 @@ namespace ts.projectSystem {
                 };
 
                 const host = createServerHost([moduleFile1, file1Consumer1, configFile, libFile]);
-                const typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+                const typingsInstaller = createTestTypingsInstaller(host);
                 const session = new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
                 openFilesForSession([moduleFile1], session);
 
@@ -337,7 +341,7 @@ namespace ts.projectSystem {
                 };
 
                 const host = createServerHost([moduleFile1, file1Consumer1, configFile, libFile]);
-                const typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+                const typingsInstaller = createTestTypingsInstaller(host);
                 const session = new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
                 openFilesForSession([moduleFile1], session);
 
@@ -359,7 +363,7 @@ namespace ts.projectSystem {
                     content: `import {y} from "./file1Consumer1";`
                 };
                 const host = createServerHost([moduleFile1, file1Consumer1, file1Consumer1Consumer1, globalFile3, configFile, libFile]);
-                const typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+                const typingsInstaller = createTestTypingsInstaller(host);
                 const session = new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
 
                 openFilesForSession([moduleFile1, file1Consumer1], session);
@@ -392,7 +396,7 @@ namespace ts.projectSystem {
                     export var t2 = 10;`
                 };
                 const host = createServerHost([file1, file2, configFile]);
-                const typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+                const typingsInstaller = createTestTypingsInstaller(host);
                 const session = new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
 
                 openFilesForSession([file1, file2], session);
@@ -475,7 +479,7 @@ namespace ts.projectSystem {
                 content: `{}`
             };
             const host = createServerHost([file1, file2, configFile, libFile]);
-            const typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+            const typingsInstaller = createTestTypingsInstaller(host);
             const session = new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
 
             openFilesForSession([file1, file2], session);
diff --git a/src/harness/unittests/tsserverProjectSystem.ts b/src/harness/unittests/tsserverProjectSystem.ts
index 5275c4c89fc..363822ca1e8 100644
--- a/src/harness/unittests/tsserverProjectSystem.ts
+++ b/src/harness/unittests/tsserverProjectSystem.ts
@@ -2,6 +2,8 @@
 /// <reference path="../../server/typingsInstaller/typingsInstaller.ts" />
 
 namespace ts.projectSystem {
+    import TI = server.typingsInstaller;
+
     const safeList = {
         path: <Path>"/safeList.json",
         content: JSON.stringify({
@@ -14,6 +16,7 @@ namespace ts.projectSystem {
     };
 
     export interface PostExecAction {
+        readonly requestKind: TI.RequestKind;
         readonly error: Error;
         readonly stdout: string;
         readonly stderr: string;
@@ -46,21 +49,27 @@ namespace ts.projectSystem {
         content: libFileContent
     };
 
-    export class TestTypingsInstaller extends server.typingsInstaller.TypingsInstaller implements server.ITypingsInstaller {
+    export class TestTypingsInstaller extends TI.TypingsInstaller implements server.ITypingsInstaller {
         protected projectService: server.ProjectService;
-        constructor(readonly globalTypingsCacheLocation: string, readonly installTypingHost: server.ServerHost) {
-            super(globalTypingsCacheLocation, safeList.path);
+        constructor(readonly globalTypingsCacheLocation: string, throttleLimit: number, readonly installTypingHost: server.ServerHost) {
+            super(globalTypingsCacheLocation, "npm", safeList.path, throttleLimit);
             this.init();
         }
 
         safeFileList = safeList.path;
         protected postExecActions: PostExecAction[] = [];
 
-        runPostExecActions() {
-            for (const action of this.postExecActions) {
+        executePendingCommands() {
+            const actionsToRun = this.postExecActions;
+            this.postExecActions = [];
+            for (const action of actionsToRun) {
                 action.callback(action.error, action.stdout, action.stderr);
             }
-            this.postExecActions = [];
+        }
+
+        checkPendingCommands(expected: TI.RequestKind[]) {
+            assert.equal(this.postExecActions.length, expected.length, `Expected ${expected.length} post install actions`);
+            this.postExecActions.forEach((act, i) => assert.equal(act.requestKind, expected[i], "Unexpected post install action"));
         }
 
         onProjectClosed(p: server.Project) {
@@ -74,16 +83,15 @@ namespace ts.projectSystem {
             return this.installTypingHost;
         }
 
-        execAsync(prefix: string, command: string, cwd: string, requestId: number, cb: (err: Error, stdout: string, stderr: string) => void): void {
-            switch (prefix) {
-                case "npm view":
-                case "npm install":
-                case "npm ls":
+        runCommand(requestKind: TI.RequestKind, requestId: number, command: string, cwd: string, cb: (err: Error, stdout: string, stderr: string) => void): void {
+            switch (requestKind) {
+                case TI.NpmViewRequest:
+                case TI.NpmInstallRequest:
                     break;
                 default:
-                    throw new Error("TypingsInstaller: execAsync command not yet implemented");
+                    assert.isTrue(false, `request ${requestKind} is not supported`);
             }
-            this.addPostExecAction("success", cb);
+            this.addPostExecAction(requestKind, "success", cb);
         }
 
         sendResponse(response: server.SetTypings | server.InvalidateCachedTypings) {
@@ -95,13 +103,14 @@ namespace ts.projectSystem {
             this.install(request);
         }
 
-        addPostExecAction(stdout: string | string[], cb: (err: Error, stdout: string, stderr: string) => void) {
+        addPostExecAction(requestKind: TI.RequestKind, stdout: string | string[], cb: TI.RequestCompletedAction) {
             const out = typeof stdout === "string" ? stdout : createNpmPackageJsonString(stdout);
             const action: PostExecAction = {
                 error: undefined,
                 stdout: out,
                 stderr: "",
-                callback: cb
+                callback: cb,
+                requestKind
             };
             this.postExecActions.push(action);
         }
@@ -152,7 +161,7 @@ namespace ts.projectSystem {
 
     export function createSession(host: server.ServerHost, typingsInstaller?: server.ITypingsInstaller) {
         if (typingsInstaller === undefined) {
-            typingsInstaller = new TestTypingsInstaller("/a/data/", host);
+            typingsInstaller = new TestTypingsInstaller("/a/data/", /*throttleLimit*/5, host);
         }
         return new server.Session(host, nullCancellationToken, /*useSingleInferredProject*/ false, typingsInstaller, Utils.byteLength, process.hrtime, nullLogger, /*canUseEvents*/ false);
     }
@@ -1643,7 +1652,7 @@ namespace ts.projectSystem {
             const host: TestServerHost & ModuleResolutionHost = createServerHost([file1, lib]);
             const resolutionTrace: string[] = [];
             host.trace = resolutionTrace.push.bind(resolutionTrace);
-            const projectService = createProjectService(host, { typingsInstaller: new TestTypingsInstaller("/a/cache", host) });
+            const projectService = createProjectService(host, { typingsInstaller: new TestTypingsInstaller("/a/cache", /*throttleLimit*/5, host) });
 
             projectService.setCompilerOptionsForInferredProjects({ traceResolution: true, allowJs: true });
             projectService.openClientFile(file1.path);
diff --git a/src/harness/unittests/typingsInstaller.ts b/src/harness/unittests/typingsInstaller.ts
index 4ff70e0d3dc..9dd1247c897 100644
--- a/src/harness/unittests/typingsInstaller.ts
+++ b/src/harness/unittests/typingsInstaller.ts
@@ -3,23 +3,47 @@
 /// <reference path="../../server/typingsInstaller/typingsInstaller.ts" />
 
 namespace ts.projectSystem {
+    import TI = server.typingsInstaller;
+
+    interface InstallerParams {
+        globalTypingsCacheLocation?: string;
+        throttleLimit?: number;
+    }
+
+    class Installer extends TestTypingsInstaller {
+        constructor(host: server.ServerHost, p?: InstallerParams) {
+            super(
+                (p && p.globalTypingsCacheLocation) || "/a/data",
+                (p && p.throttleLimit) || 5,
+                host);
+        }
+
+        installAll(expectedView: typeof TI.NpmViewRequest[], expectedInstall: typeof TI.NpmInstallRequest[]) {
+            this.checkPendingCommands(expectedView);
+            this.executePendingCommands();
+            this.checkPendingCommands(expectedInstall);
+            this.executePendingCommands();
+        }
+    }
+
     describe("typingsInstaller", () => {
-        function execHelper(self: TestTypingsInstaller, host: TestServerHost, installedTypings: string[], typingFiles: FileOrFolder[], prefix: string, cb: (err: Error, stdout: string, stderr: string) => void): boolean {
-            let execSuper = true;
-            switch (prefix) {
-                case "npm install":
-                    for (const file of typingFiles) {
-                        host.createFileOrFolder(file, /*createParentDirectory*/ true);
-                    }
+        function executeCommand(self: Installer, host: TestServerHost, installedTypings: string[], typingFiles: FileOrFolder[], requestKind: TI.RequestKind, cb: TI.RequestCompletedAction): void {
+            switch (requestKind) {
+                case TI.NpmInstallRequest:
+                    self.addPostExecAction(requestKind, installedTypings, (err, stdout, stderr) => {
+                        for (const file of typingFiles) {
+                            host.createFileOrFolder(file, /*createParentDirectory*/ true);
+                        }
+                        cb(err, stdout, stderr);
+                    });
                     break;
-                case "npm ls":
-                    self.addPostExecAction(installedTypings, cb);
-                    execSuper = false;
+                case TI.NpmViewRequest:
+                    self.addPostExecAction(requestKind, installedTypings, cb);
                     break;
                 default:
+                    assert.isTrue(false, `unexpected request kind ${requestKind}`);
                     break;
             }
-            return execSuper;
         }
         it("configured projects (typings installed) 1", () => {
             const file1 = {
@@ -52,16 +76,14 @@ namespace ts.projectSystem {
                 content: "declare const $: { x: number }"
             };
             const host = createServerHost([file1, tsconfig, packageJson]);
-            const installer = new (class extends TestTypingsInstaller {
+            const installer = new (class extends Installer {
                 constructor() {
-                    super("/a/data/", host);
+                    super(host);
                 }
-                execAsync(prefix: string, command: string, cwd: string, requestId: number, cb: (err: Error, stdout: string, stderr: string) => void): void {
+                runCommand(requestKind: TI.RequestKind, requestId: number, command: string, cwd: string, cb: server.typingsInstaller.RequestCompletedAction) {
                     const installedTypings = ["@types/jquery"];
                     const typingFiles = [jquery];
-                    if (execHelper(this, host, installedTypings, typingFiles, prefix, cb)) {
-                        super.execAsync(prefix, command, cwd, requestId, cb);
-                    }
+                    executeCommand(this, host, installedTypings, typingFiles, requestKind, cb);
                 }
             })();
 
@@ -72,9 +94,7 @@ namespace ts.projectSystem {
             const p = projectService.configuredProjects[0];
             checkProjectActualFiles(p, [file1.path]);
 
-            assert(host.fileExists(combinePaths(installer.globalTypingsCacheLocation, "package.json")));
-
-            installer.runPostExecActions();
+            installer.installAll([TI.NpmViewRequest], [TI.NpmInstallRequest]);
 
             checkNumberOfProjects(projectService, { configuredProjects: 1 });
             checkProjectActualFiles(p, [file1.path, jquery.path]);
@@ -100,16 +120,14 @@ namespace ts.projectSystem {
                 content: "declare const $: { x: number }"
             };
             const host = createServerHost([file1, packageJson]);
-            const installer = new (class extends TestTypingsInstaller {
+            const installer = new (class extends Installer {
                 constructor() {
-                    super("/a/data/", host);
+                    super(host);
                 }
-                execAsync(prefix: string, command: string, cwd: string, requestId: number, cb: (err: Error, stdout: string, stderr: string) => void): void {
+                runCommand(requestKind: TI.RequestKind, requestId: number, command: string, cwd: string, cb: server.typingsInstaller.RequestCompletedAction) {
                     const installedTypings = ["@types/jquery"];
                     const typingFiles = [jquery];
-                    if (execHelper(this, host, installedTypings, typingFiles, prefix, cb)) {
-                        super.execAsync(prefix, command, cwd, requestId, cb);
-                    }
+                    executeCommand(this, host, installedTypings, typingFiles, requestKind, cb);
                 }
             })();
 
@@ -120,9 +138,7 @@ namespace ts.projectSystem {
             const p = projectService.inferredProjects[0];
             checkProjectActualFiles(p, [file1.path]);
 
-            assert(host.fileExists(combinePaths(installer.globalTypingsCacheLocation, "package.json")));
-
-            installer.runPostExecActions();
+            installer.installAll([TI.NpmViewRequest], [TI.NpmInstallRequest]);
 
             checkNumberOfProjects(projectService, { inferredProjects: 1 });
             checkProjectActualFiles(p, [file1.path, jquery.path]);
@@ -134,9 +150,9 @@ namespace ts.projectSystem {
                 content: ""
             };
             const host = createServerHost([file1]);
-            const installer = new (class extends TestTypingsInstaller {
+            const installer = new (class extends Installer {
                 constructor() {
-                    super("", host);
+                    super(host);
                 }
                 enqueueInstallTypingsRequest() {
                     assert(false, "auto discovery should not be enabled");
@@ -150,6 +166,7 @@ namespace ts.projectSystem {
                 options: {},
                 rootFiles: [toExternalFile(file1.path)]
             });
+            installer.checkPendingCommands([]);
             // by default auto discovery will kick in if project contain only .js/.d.ts files
             // in this case project contain only ts files - no auto discovery
             projectService.checkNumberOfProjects({ externalProjects: 1 });
@@ -161,9 +178,9 @@ namespace ts.projectSystem {
                 content: ""
             };
             const host = createServerHost([file1]);
-            const installer = new (class extends TestTypingsInstaller {
+            const installer = new (class extends Installer {
                 constructor() {
-                    super("", host);
+                    super(host);
                 }
                 enqueueInstallTypingsRequest() {
                     assert(false, "auto discovery should not be enabled");
@@ -178,6 +195,7 @@ namespace ts.projectSystem {
                 rootFiles: [toExternalFile(file1.path)],
                 typingOptions: { include: ["jquery"] }
             });
+            installer.checkPendingCommands([]);
             // by default auto discovery will kick in if project contain only .js/.d.ts files
             // in this case project contain only ts files - no auto discovery even if typing options is set
             projectService.checkNumberOfProjects({ externalProjects: 1 });
@@ -194,24 +212,18 @@ namespace ts.projectSystem {
             };
             const host = createServerHost([file1]);
             let enqueueIsCalled = false;
-            let runInstallIsCalled = false;
-            const installer = new (class extends TestTypingsInstaller {
+            const installer = new (class extends Installer {
                 constructor() {
-                    super("", host);
+                    super(host);
                 }
                 enqueueInstallTypingsRequest(project: server.Project, typingOptions: TypingOptions) {
                     enqueueIsCalled = true;
                     super.enqueueInstallTypingsRequest(project, typingOptions);
                 }
-                execAsync(prefix: string, command: string, cwd: string, requestId: number, cb: (err: Error, stdout: string, stderr: string) => void): void {
+                runCommand(requestKind: TI.RequestKind, requestId: number, command: string, cwd: string, cb: TI.RequestCompletedAction): void {
                     const installedTypings = ["@types/jquery"];
                     const typingFiles = [jquery];
-                    if (execHelper(this, host, installedTypings, typingFiles, prefix, cb)) {
-                        super.execAsync(prefix, command, cwd, requestId, cb);
-                    }
-                    if (prefix === "npm install") {
-                        runInstallIsCalled = true;
-                    }
+                    executeCommand(this, host, installedTypings, typingFiles, requestKind, cb);
                 }
             })();
 
@@ -224,12 +236,11 @@ namespace ts.projectSystem {
                 typingOptions: { enableAutoDiscovery: true, include: ["node"] }
             });
 
-            installer.runPostExecActions();
+            assert.isTrue(enqueueIsCalled, "expected enqueueIsCalled to be true");
+            installer.installAll([TI.NpmViewRequest], [TI.NpmInstallRequest]);
 
             // autoDiscovery is set in typing options - use it even if project contains only .ts files
             projectService.checkNumberOfProjects({ externalProjects: 1 });
-            assert.isTrue(enqueueIsCalled, "expected 'enqueueIsCalled' to be true");
-            assert.isTrue(runInstallIsCalled, "expected 'runInstallIsCalled' to be true");
         });
 
         it("external project - no typing options, with only js, jsx, d.ts files", () => {
@@ -259,16 +270,14 @@ namespace ts.projectSystem {
             };
 
             const host = createServerHost([file1, file2, file3]);
-            const installer = new (class extends TestTypingsInstaller {
+            const installer = new (class extends Installer {
                 constructor() {
-                    super("/a/data/", host);
+                    super(host);
                 }
-                execAsync(prefix: string, command: string, cwd: string, requestId: number, cb: (err: Error, stdout: string, stderr: string) => void): void {
+                runCommand(requestKind: TI.RequestKind, requestId: number, command: string, cwd: string, cb: TI.RequestCompletedAction): void {
                     const installedTypings = ["@types/lodash", "@types/react"];
                     const typingFiles = [lodash, react];
-                    if (execHelper(this, host, installedTypings, typingFiles, prefix, cb)) {
-                        super.execAsync(prefix, command, cwd, requestId, cb);
-                    }
+                    executeCommand(this, host, installedTypings, typingFiles, requestKind, cb);
                 }
             })();
 
@@ -285,7 +294,7 @@ namespace ts.projectSystem {
             projectService.checkNumberOfProjects({ externalProjects: 1 });
             checkProjectActualFiles(p, [file1.path, file2.path, file3.path]);
 
-            installer.runPostExecActions();
+            installer.installAll([TI.NpmViewRequest, TI.NpmViewRequest], [TI.NpmInstallRequest], );
 
             checkNumberOfProjects(projectService, { externalProjects: 1 });
             checkProjectActualFiles(p, [file1.path, file2.path, file3.path, lodash.path, react.path]);
@@ -305,24 +314,18 @@ namespace ts.projectSystem {
 
             const host = createServerHost([file1, file2]);
             let enqueueIsCalled = false;
-            let runInstallIsCalled = false;
-            const installer = new (class extends TestTypingsInstaller {
+            const installer = new (class extends Installer {
                 constructor() {
-                    super("/a/data/", host);
+                    super(host);
                 }
                 enqueueInstallTypingsRequest(project: server.Project, typingOptions: TypingOptions) {
                     enqueueIsCalled = true;
                     super.enqueueInstallTypingsRequest(project, typingOptions);
                 }
-                execAsync(prefix: string, command: string, cwd: string, requestId: number, cb: (err: Error, stdout: string, stderr: string) => void): void {
+                runCommand(requestKind: TI.RequestKind, requestId: number, command: string, cwd: string, cb: TI.RequestCompletedAction): void {
                     const installedTypings: string[] = [];
                     const typingFiles: FileOrFolder[] = [];
-                    if (execHelper(this, host, installedTypings, typingFiles, prefix, cb)) {
-                        super.execAsync(prefix, command, cwd, requestId, cb);
-                    }
-                    if (prefix === "npm install") {
-                        runInstallIsCalled = true;
-                    }
+                    executeCommand(this, host, installedTypings, typingFiles, requestKind, cb);
                 }
             })();
 
@@ -339,12 +342,10 @@ namespace ts.projectSystem {
             projectService.checkNumberOfProjects({ externalProjects: 1 });
             checkProjectActualFiles(p, [file1.path, file2.path]);
 
-            installer.runPostExecActions();
+            installer.checkPendingCommands([]);
 
             checkNumberOfProjects(projectService, { externalProjects: 1 });
             checkProjectActualFiles(p, [file1.path, file2.path]);
-            assert.isFalse(enqueueIsCalled, "expected 'enqueueIsCalled' to be false");
-            assert.isFalse(runInstallIsCalled, "expected 'runInstallIsCalled' to be false");
         });
 
         it("external project - with typing options, with only js, d.ts files", () => {
@@ -392,16 +393,14 @@ namespace ts.projectSystem {
             };
 
             const host = createServerHost([file1, file2, file3, packageJson]);
-            const installer = new (class extends TestTypingsInstaller {
+            const installer = new (class extends Installer {
                 constructor() {
-                    super("/a/data/", host);
+                    super(host);
                 }
-                execAsync(prefix: string, command: string, cwd: string, requestId: number, cb: (err: Error, stdout: string, stderr: string) => void): void {
+                runCommand(requestKind: TI.RequestKind, requestId: number, command: string, cwd: string, cb: TI.RequestCompletedAction): void {
                     const installedTypings = ["@types/commander", "@types/express", "@types/jquery", "@types/moment"];
                     const typingFiles = [commander, express, jquery, moment];
-                    if (execHelper(this, host, installedTypings, typingFiles, prefix, cb)) {
-                        super.execAsync(prefix, command, cwd, requestId, cb);
-                    }
+                    executeCommand(this, host, installedTypings, typingFiles, requestKind, cb);
                 }
             })();
 
@@ -418,18 +417,21 @@ namespace ts.projectSystem {
             projectService.checkNumberOfProjects({ externalProjects: 1 });
             checkProjectActualFiles(p, [file1.path, file2.path, file3.path]);
 
-            installer.runPostExecActions();
+            installer.installAll(
+                [TI.NpmViewRequest, TI.NpmViewRequest, TI.NpmViewRequest, TI.NpmViewRequest],
+                [TI.NpmInstallRequest]
+            );
 
             checkNumberOfProjects(projectService, { externalProjects: 1 });
             checkProjectActualFiles(p, [file1.path, file2.path, file3.path, commander.path, express.path, jquery.path, moment.path]);
         });
 
         it("Throttle - delayed typings to install", () => {
-            const file1 = {
+            const lodashJs = {
                 path: "/a/b/lodash.js",
                 content: ""
             };
-            const file2 = {
+            const commanderJs = {
                 path: "/a/b/commander.js",
                 content: ""
             };
@@ -442,11 +444,7 @@ namespace ts.projectSystem {
                 content: JSON.stringify({
                     name: "test",
                     dependencies: {
-                        express: "^3.1.0",
-                        cordova: "1.0.0",
-                        grunt: "1.0.0",
-                        gulp: "1.0.0",
-                        forever: "1.0.0",
+                        express: "^3.1.0"
                     }
                 })
             };
@@ -471,42 +469,16 @@ namespace ts.projectSystem {
                 path: "/a/data/node_modules/@types/lodash/index.d.ts",
                 content: "declare const lodash: { x: number }"
             };
-            const cordova = {
-                path: "/a/data/node_modules/@types/cordova/index.d.ts",
-                content: "declare const cordova: { x: number }"
-            };
-            const grunt = {
-                path: "/a/data/node_modules/@types/grunt/index.d.ts",
-                content: "declare const grunt: { x: number }"
-            };
-            const gulp = {
-                path: "/a/data/node_modules/@types/gulp/index.d.ts",
-                content: "declare const gulp: { x: number }"
-            };
-           const forever = {
-                path: "/a/data/node_modules/@types/forever/index.d.ts",
-                content: "declare const forever: { x: number }"
-            };
 
-            let npmViewCount = 0;
-            let npmInstallCount = 0;
-            const host = createServerHost([file1, file2, file3, packageJson]);
-            const installer = new (class extends TestTypingsInstaller {
+            const typingFiles = [commander, express, jquery, moment, lodash];
+            const host = createServerHost([lodashJs, commanderJs, file3, packageJson]);
+            const installer = new (class extends Installer {
                 constructor() {
-                    super("/a/data/", host);
+                    super(host, { throttleLimit: 3 });
                 }
-                execAsync(prefix: string, command: string, cwd: string, requestId: number, cb: (err: Error, stdout: string, stderr: string) => void): void {
-                    if (prefix === "npm view") {
-                        npmViewCount++;
-                    }
-                     if (prefix === "npm install") {
-                        npmInstallCount++;
-                    }
-                    const installedTypings = ["@types/commander", "@types/express", "@types/jquery", "@types/moment", "@types/lodash", "@types/cordova", "@types/grunt", "@types/gulp", "@types/forever"];
-                    const typingFiles = [commander, express, jquery, moment, lodash, cordova, grunt, gulp, forever];
-                    if (execHelper(this, host, installedTypings, typingFiles, prefix, cb)) {
-                        super.execAsync(prefix, command, cwd, requestId, cb);
-                    }
+                runCommand(requestKind: TI.RequestKind, requestId: number, command: string, cwd: string, cb: TI.RequestCompletedAction): void {
+                    const installedTypings = ["@types/commander", "@types/express", "@types/jquery", "@types/moment", "@types/lodash"];
+                    executeCommand(this, host, installedTypings, typingFiles, requestKind, cb);
                 }
             })();
 
@@ -515,33 +487,41 @@ namespace ts.projectSystem {
             projectService.openExternalProject({
                 projectFileName,
                 options: { allowJS: true, moduleResolution: ModuleResolutionKind.NodeJs },
-                rootFiles: [toExternalFile(file1.path), toExternalFile(file2.path), toExternalFile(file3.path)],
+                rootFiles: [toExternalFile(lodashJs.path), toExternalFile(commanderJs.path), toExternalFile(file3.path)],
                 typingOptions: { include: ["jquery", "moment"] }
             });
 
             const p = projectService.externalProjects[0];
             projectService.checkNumberOfProjects({ externalProjects: 1 });
-            checkProjectActualFiles(p, [file1.path, file2.path, file3.path]);
-            // The npm view count should be 5 even though there are 9 typings to acquire.
-            // The throttle limit has been reached so no more execAsync requests will be 
-            // queued until these have been processed. 
-            assert.isTrue(npmViewCount === 5);
-            assert.isTrue(npmInstallCount === 0);
+            checkProjectActualFiles(p, [lodashJs.path, commanderJs.path, file3.path]);
+            // expected 3 view requests in the queue
+            installer.checkPendingCommands([TI.NpmViewRequest, TI.NpmViewRequest, TI.NpmViewRequest]);
+            assert.equal(installer.pendingRunRequests.length, 2, "expected 2 pending requests");
 
-            installer.runPostExecActions();
+            // push view requests
+            installer.executePendingCommands();
+            // expected 2 remaining view requests in the queue
+            installer.checkPendingCommands([TI.NpmViewRequest, TI.NpmViewRequest]);
+            // push view requests
+            installer.executePendingCommands();
+            // expected one install request
+            installer.checkPendingCommands([TI.NpmInstallRequest]);
+            installer.executePendingCommands();
+            // expected all typings file to exist
+            for (const f of typingFiles) {
+                assert.isTrue(host.fileExists(f.path), `expected file ${f.path} to exist`);
+            }
 
-            assert.isTrue(npmViewCount === 9);
-            assert.isTrue(npmInstallCount === 1);
             checkNumberOfProjects(projectService, { externalProjects: 1 });
-            checkProjectActualFiles(p, [file1.path, file2.path, file3.path, commander.path, express.path, jquery.path, moment.path, lodash.path, cordova.path, grunt.path, gulp.path, forever.path]);
+            checkProjectActualFiles(p, [lodashJs.path, commanderJs.path, file3.path, commander.path, express.path, jquery.path, moment.path, lodash.path]);
         });
 
         it("Throttle - delayed run install requests", () => {
-            const file1 = {
+            const lodashJs = {
                 path: "/a/b/lodash.js",
                 content: ""
             };
-            const file2 = {
+            const commanderJs = {
                 path: "/a/b/commander.js",
                 content: ""
             };
@@ -552,119 +532,100 @@ namespace ts.projectSystem {
 
             const commander = {
                 path: "/a/data/node_modules/@types/commander/index.d.ts",
-                content: "declare const commander: { x: number }"
-            };
-            const express = {
-                path: "/a/data/node_modules/@types/express/index.d.ts",
-                content: "declare const express: { x: number }"
+                content: "declare const commander: { x: number }",
+                typings: "@types/commander"
             };
             const jquery = {
                 path: "/a/data/node_modules/@types/jquery/index.d.ts",
-                content: "declare const jquery: { x: number }"
-            };
-            const moment = {
-                path: "/a/data/node_modules/@types/moment/index.d.ts",
-                content: "declare const moment: { x: number }"
+                content: "declare const jquery: { x: number }",
+                typings: "@types/jquery"
             };
             const lodash = {
                 path: "/a/data/node_modules/@types/lodash/index.d.ts",
-                content: "declare const lodash: { x: number }"
+                content: "declare const lodash: { x: number }",
+                typings: "@types/lodash"
             };
             const cordova = {
                 path: "/a/data/node_modules/@types/cordova/index.d.ts",
-                content: "declare const cordova: { x: number }"
+                content: "declare const cordova: { x: number }",
+                typings: "@types/cordova"
             };
             const grunt = {
                 path: "/a/data/node_modules/@types/grunt/index.d.ts",
-                content: "declare const grunt: { x: number }"
+                content: "declare const grunt: { x: number }",
+                typings: "@types/grunt"
             };
             const gulp = {
                 path: "/a/data/node_modules/@types/gulp/index.d.ts",
-                content: "declare const gulp: { x: number }"
-            };
-           const forever = {
-                path: "/a/data/node_modules/@types/forever/index.d.ts",
-                content: "declare const forever: { x: number }"
+                content: "declare const gulp: { x: number }",
+                typings: "@types/gulp"
             };
 
-            let npmViewCount = 0;
-            let npmInstallCount = 0;
-            let hasRunInstall2Typings = false;
-            const host = createServerHost([file1, file2, file3]);
-            const installer = new (class extends TestTypingsInstaller {
+            const host = createServerHost([lodashJs, commanderJs, file3]);
+            const installer = new (class extends Installer {
                 constructor() {
-                    super("/a/data/", host);
+                    super(host, { throttleLimit: 3 });
                 }
-                execAsync(prefix: string, command: string, cwd: string, requestId: number, cb: (err: Error, stdout: string, stderr: string) => void): void {
-                    switch (prefix) {
-                        case "npm view":
-                            if (command.match("grunt|gulp|forever")) {
-                                hasRunInstall2Typings = true;
-                            }
-                            npmViewCount++;
-                            break;
-                        case "npm install":
-                            npmInstallCount++;
-                            break;
-                    }
-
-                    let installedTypings: string[];
-                    let typingFiles: FileOrFolder[];
-                    if (npmInstallCount <= 1) {
-                        installedTypings = ["@types/commander", "@types/express", "@types/jquery", "@types/moment", "@types/lodash", "@types/cordova"];
-                        typingFiles = [commander, express, jquery, moment, lodash, cordova];
+                runCommand(requestKind: TI.RequestKind, requestId: number, command: string, cwd: string, cb: TI.RequestCompletedAction): void {
+                    if (requestKind === TI.NpmInstallRequest) {
+                        let typingFiles: (FileOrFolder & { typings: string}) [] = [];
+                        if (command.indexOf("commander") >= 0) {
+                            typingFiles = [commander, jquery, lodash, cordova];
+                        }
+                        else {
+                            typingFiles = [grunt, gulp];
+                        }
+                        executeCommand(this, host, typingFiles.map(f => f.typings), typingFiles, requestKind, cb);
                     }
                     else {
-                        installedTypings = ["@types/grunt", "@types/gulp", "@types/forever"];
-                        typingFiles = [grunt, gulp, forever];
-                    }
-
-                    if (execHelper(this, host, installedTypings, typingFiles, prefix, cb)) {
-                        super.execAsync(prefix, command, cwd, requestId, cb);
+                        executeCommand(this, host, [], [], requestKind, cb);
                     }
                 }
             })();
 
-            // Create project #1 with 6 typings
+            // Create project #1 with 4 typings
             const projectService = createProjectService(host, { typingsInstaller: installer });
             const projectFileName1 = "/a/app/test1.csproj";
             projectService.openExternalProject({
                 projectFileName: projectFileName1,
                 options: { allowJS: true, moduleResolution: ModuleResolutionKind.NodeJs },
-                rootFiles: [toExternalFile(file1.path), toExternalFile(file2.path), toExternalFile(file3.path)],
-                typingOptions: { include: ["jquery", "moment", "express", "cordova"] }
+                rootFiles: [toExternalFile(lodashJs.path), toExternalFile(commanderJs.path), toExternalFile(file3.path)],
+                typingOptions: { include: ["jquery", "cordova" ] }
             });
 
-            // Create project #2 with 3 typings
+            installer.checkPendingCommands([TI.NpmViewRequest, TI.NpmViewRequest, TI.NpmViewRequest]);
+            assert.equal(installer.pendingRunRequests.length, 1, "expect one throttled request");
+
+            // Create project #2 with 2 typings
             const projectFileName2 = "/a/app/test2.csproj";
             projectService.openExternalProject({
                 projectFileName: projectFileName2,
                 options: { allowJS: true, moduleResolution: ModuleResolutionKind.NodeJs },
                 rootFiles: [toExternalFile(file3.path)],
-                typingOptions: { include: ["grunt", "gulp", "forever"] }
+                typingOptions: { include: ["grunt", "gulp"] }
             });
+            assert.equal(installer.pendingRunRequests.length, 3, "expect three throttled request");
 
             const p1 = projectService.externalProjects[0];
             const p2 = projectService.externalProjects[1];
             projectService.checkNumberOfProjects({ externalProjects: 2 });
-            checkProjectActualFiles(p1, [file1.path, file2.path, file3.path]);
+            checkProjectActualFiles(p1, [lodashJs.path, commanderJs.path, file3.path]);
             checkProjectActualFiles(p2, [file3.path]);
 
-            // The npm view count should be 5 even though there are 9 typings to acquire.
-            // The throttle limit has been reached so no more run execAsync requests will be 
-            // queued until these have been processed. Assert that typings from the second 
-            // run install request have not been queued.
-            assert.isTrue(npmViewCount === 5);
-            assert.isTrue(npmInstallCount === 0);
-            assert.isFalse(hasRunInstall2Typings);
 
-            installer.runPostExecActions();
+            installer.executePendingCommands();
+            // expected one view request from the first project and two - from the second one
+            installer.checkPendingCommands([TI.NpmViewRequest, TI.NpmViewRequest, TI.NpmViewRequest]);
+            assert.equal(installer.pendingRunRequests.length, 0, "expected no throttled requests");
 
-            assert.isTrue(npmViewCount === 9);
-            assert.isTrue(npmInstallCount === 2);
-            assert.isTrue(hasRunInstall2Typings);
-            checkProjectActualFiles(p1, [file1.path, file2.path, file3.path, commander.path, express.path, jquery.path, moment.path, lodash.path, cordova.path]);
-            checkProjectActualFiles(p2, [file3.path, grunt.path, gulp.path, forever.path]);
+            installer.executePendingCommands();
+
+            // should be two install requests from both projects
+            installer.checkPendingCommands([TI.NpmInstallRequest, TI.NpmInstallRequest]);
+            installer.executePendingCommands();
+
+            checkProjectActualFiles(p1, [lodashJs.path, commanderJs.path, file3.path, commander.path, jquery.path, lodash.path, cordova.path]);
+            checkProjectActualFiles(p2, [file3.path, grunt.path, gulp.path ]);
         });
     });
 }
\ No newline at end of file
diff --git a/src/server/typingsInstaller/nodeTypingsInstaller.ts b/src/server/typingsInstaller/nodeTypingsInstaller.ts
index 3dc4be7e3da..7df1e9a7877 100644
--- a/src/server/typingsInstaller/nodeTypingsInstaller.ts
+++ b/src/server/typingsInstaller/nodeTypingsInstaller.ts
@@ -6,6 +6,11 @@ namespace ts.server.typingsInstaller {
         appendFileSync(file: string, content: string): void
     } = require("fs");
 
+    const path: {
+        join(...parts: string[]): string;
+        dirname(path: string): string;
+    } = require("path");
+
     class FileLog implements Log {
         constructor(private readonly logFile?: string) {
         }
@@ -19,12 +24,17 @@ namespace ts.server.typingsInstaller {
     }
 
     export class NodeTypingsInstaller extends TypingsInstaller {
-        private exec: { (command: string, options: { cwd: string }, callback?: (error: Error, stdout: string, stderr: string) => void): any };
+        private readonly exec: { (command: string, options: { cwd: string }, callback?: (error: Error, stdout: string, stderr: string) => void): any };
 
         readonly installTypingHost: InstallTypingHost = sys;
 
-        constructor(globalTypingsCacheLocation: string, log: Log) {
-            super(globalTypingsCacheLocation, toPath("typingSafeList.json", __dirname, createGetCanonicalFileName(sys.useCaseSensitiveFileNames)), log);
+        constructor(globalTypingsCacheLocation: string, throttleLimit: number, log: Log) {
+            super(
+                globalTypingsCacheLocation,
+                /*npmPath*/ `"${path.join(path.dirname(process.argv[0]), "npm")}"`,
+                toPath("typingSafeList.json", __dirname, createGetCanonicalFileName(sys.useCaseSensitiveFileNames)),
+                throttleLimit,
+                log);
             if (this.log.isEnabled()) {
                 this.log.writeLine(`Process id: ${process.pid}`);
             }
@@ -55,16 +65,16 @@ namespace ts.server.typingsInstaller {
             }
         }
 
-        protected execAsync(prefix: string, command: string, cwd: string, requestId: number, cb: (err: Error, stdout: string, stderr: string) => void) {
+        protected runCommand(requestKind: RequestKind, requestId: number, command: string, cwd: string, onRequestCompleted: RequestCompletedAction): void {
             if (this.log.isEnabled()) {
                 this.log.writeLine(`#${requestId} running command '${command}'.`);
             }
             this.exec(command, { cwd }, (err, stdout, stderr) => {
                 if (this.log.isEnabled()) {
-                    this.log.writeLine(`${prefix} #${requestId} stdout: ${stdout}`);
-                    this.log.writeLine(`${prefix} #${requestId} stderr: ${stderr}`);
+                    this.log.writeLine(`${requestKind} #${requestId} stdout: ${stdout}`);
+                    this.log.writeLine(`${requestKind} #${requestId} stderr: ${stderr}`);
                 }
-                cb(err, stdout, stderr);
+                onRequestCompleted(err, stdout, stderr);
             });
         }
     }
@@ -90,6 +100,6 @@ namespace ts.server.typingsInstaller {
         }
         process.exit(0);
     });
-    const installer = new NodeTypingsInstaller(globalTypingsCacheLocation, log);
+    const installer = new NodeTypingsInstaller(globalTypingsCacheLocation, /*throttleLimit*/5, log);
     installer.init();
 }
\ No newline at end of file
diff --git a/src/server/typingsInstaller/typingsInstaller.ts b/src/server/typingsInstaller/typingsInstaller.ts
index 24139436932..1113e6e2701 100644
--- a/src/server/typingsInstaller/typingsInstaller.ts
+++ b/src/server/typingsInstaller/typingsInstaller.ts
@@ -8,19 +8,11 @@ namespace ts.server.typingsInstaller {
         devDependencies: MapLike<any>;
     }
 
-    interface RunInstallRequest {
-        readonly cachePath: string;
-        readonly typingsToInstall: string[];
-        readonly postInstallAction: (installedTypings: string[]) => void;
-    }
-
     export interface Log {
         isEnabled(): boolean;
         writeLine(text: string): void;
     }
 
-    const throttleLimit = 5;
-
     const nullLog: Log = {
         isEnabled: () => false,
         writeLine: () => {}
@@ -31,27 +23,44 @@ namespace ts.server.typingsInstaller {
         return result.resolvedModule && result.resolvedModule.resolvedFileName;
     }
 
+    export const NpmViewRequest: "npm view" = "npm view";
+    export const NpmInstallRequest: "npm install" = "npm install";
+
+    export type RequestKind = typeof NpmViewRequest | typeof NpmInstallRequest;
+
+    export type RequestCompletedAction = (err: Error, stdout: string, stderr: string) => void;
+    type PendingRequest = {
+        requestKind: RequestKind;
+        requestId: number;
+        command: string;
+        cwd: string;
+        onRequestCompleted: RequestCompletedAction
+    };
+
     export abstract class TypingsInstaller {
+        private readonly packageNameToTypingLocation: Map<string> = createMap<string>();
+        private readonly missingTypingsSet: Map<true> = createMap<true>();
+        private readonly knownCachesSet: Map<true> = createMap<true>();
+        private readonly projectWatchers: Map<FileWatcher[]> = createMap<FileWatcher[]>();
+        readonly pendingRunRequests: PendingRequest[] = [];
+
         private installRunCount = 1;
-        private throttleCount = 0;
-        private packageNameToTypingLocation: Map<string> = createMap<string>();
-        private missingTypingsSet: Map<true> = createMap<true>();
-        private knownCachesSet: Map<true> = createMap<true>();
-        private projectWatchers: Map<FileWatcher[]> = createMap<FileWatcher[]>();
-        private delayedRunInstallRequests: RunInstallRequest[] = [];
-        private npmPath: string;
+        private inFlightRequestCount = 0;
 
         abstract readonly installTypingHost: InstallTypingHost;
 
-        constructor(readonly globalCachePath: string, readonly safeListPath: Path, protected readonly log = nullLog) {
+        constructor(
+            readonly globalCachePath: string,
+            readonly npmPath: string,
+            readonly safeListPath: Path,
+            readonly throttleLimit: number,
+            protected readonly log = nullLog) {
             if (this.log.isEnabled()) {
                 this.log.writeLine(`Global cache location '${globalCachePath}', safe file path '${safeListPath}'`);
             }
         }
 
         init() {
-            const path = require("path");
-            this.npmPath = `"${path.join(path.dirname(process.argv[0]), "npm")}"`;
             this.processCacheLocation(this.globalCachePath);
         }
 
@@ -239,77 +248,37 @@ namespace ts.server.typingsInstaller {
         }
 
         private runInstall(cachePath: string, typingsToInstall: string[], postInstallAction: (installedTypings: string[]) => void): void {
-            if (this.throttleCount === throttleLimit) {
-                const request = {
-                    cachePath: cachePath,
-                    typingsToInstall: typingsToInstall,
-                    postInstallAction: postInstallAction
-                };
-                this.delayedRunInstallRequests.push(request);
-                return;
-            }
-            const id = this.installRunCount;
+            const requestId = this.installRunCount;
+
             this.installRunCount++;
             let execInstallCmdCount = 0;
             const filteredTypings: string[] = [];
-            const delayedTypingsToInstall: string[] = [];
             for (const typing of typingsToInstall) {
-                if (this.throttleCount === throttleLimit) {
-                    delayedTypingsToInstall.push(typing);
-                    continue;
-                }
                 execNpmViewTyping(this, typing);
             }
 
             function execNpmViewTyping(self: TypingsInstaller, typing: string) {
-                self.throttleCount++;
                 const command = `${self.npmPath} view @types/${typing} --silent name`;
-                self.execAsync("npm view", command, cachePath, id, (err, stdout, stderr) => {
+                self.execAsync(NpmViewRequest, requestId, command, cachePath, (err, stdout, stderr) => {
                     if (stdout) {
                         filteredTypings.push(typing);
                     }
                     execInstallCmdCount++;
-                    self.throttleCount--;
-                    if (delayedTypingsToInstall.length > 0) {
-                        return execNpmViewTyping(self, delayedTypingsToInstall.pop());
-                    }
                     if (execInstallCmdCount === typingsToInstall.length) {
                         installFilteredTypings(self, filteredTypings);
-                        if (self.delayedRunInstallRequests.length > 0) {
-                            const request = self.delayedRunInstallRequests.pop();
-                            return self.runInstall(request.cachePath, request.typingsToInstall, request.postInstallAction);
-                        }
                     }
                 });
             }
 
             function installFilteredTypings(self: TypingsInstaller, filteredTypings: string[]) {
                 if (filteredTypings.length === 0) {
-                    reportInstalledTypings(self);
+                    postInstallAction([]);
                     return;
                 }
-                const command = `${self.npmPath} install ${filteredTypings.map(t => "@types/" + t).join(" ")} --save-dev`;
-                self.execAsync("npm install", command, cachePath, id, (err, stdout, stderr) => {
-                    if (stdout) {
-                        reportInstalledTypings(self);
-                    }
-                });
-            }
-
-            function reportInstalledTypings(self: TypingsInstaller) {
-                const command = `${self.npmPath} ls -json`;
-                self.execAsync("npm ls", command, cachePath, id, (err, stdout, stderr) => {
-                    let installedTypings: string[];
-                    try {
-                        const response = JSON.parse(stdout);
-                        if (response.dependencies) {
-                            installedTypings = getOwnKeys(response.dependencies);
-                        }
-                    }
-                    catch (e) {
-                        self.log.writeLine(`Error parsing installed @types dependencies. Error details: ${e.message}`);
-                    }
-                    postInstallAction(installedTypings || []);
+                const scopedTypings = filteredTypings.map(t => "@types/" + t);
+                const command = `${self.npmPath} install ${scopedTypings.join(" ")} --save-dev`;
+                self.execAsync(NpmInstallRequest, requestId, command, cachePath, (err, stdout, stderr) => {
+                    postInstallAction(stdout ? scopedTypings : []);
                 });
             }
         }
@@ -357,7 +326,24 @@ namespace ts.server.typingsInstaller {
             };
         }
 
-        protected abstract execAsync(prefix: string, command: string, cwd: string, requestId: number, cb: (err: Error, stdout: string, stderr: string) => void): void;
+        private execAsync(requestKind: RequestKind, requestId: number, command: string, cwd: string, onRequestCompleted: RequestCompletedAction): void {
+            this.pendingRunRequests.unshift({ requestKind, requestId, command, cwd, onRequestCompleted });
+            this.executeWithThrottling();
+        }
+
+        private executeWithThrottling() {
+            while (this.inFlightRequestCount < this.throttleLimit && this.pendingRunRequests.length) {
+                this.inFlightRequestCount++;
+                const request = this.pendingRunRequests.pop();
+                this.runCommand(request.requestKind, request.requestId, request.command, request.cwd, (err, stdout, stderr) => {
+                    this.inFlightRequestCount--;
+                    request.onRequestCompleted(err, stdout, stderr);
+                    this.executeWithThrottling();
+                });
+            }
+        }
+
+        protected abstract runCommand(requestKind: RequestKind, requestId: number, command: string, cwd: string, onRequestCompleted: RequestCompletedAction): void;
         protected abstract sendResponse(response: SetTypings | InvalidateCachedTypings): void;
     }
 }
\ No newline at end of file