Move util.now() implementation into platform. (tensorflow#1834)

FEATURE

Author: Nikhil Thorat

src/platforms/platform.ts

@@ -29,6 +29,13 @@ export interface Platform {
    */
   fetch(path: string, requestInits?: RequestInit): Promise<Response>;
 
+  /**
+   * Returns the current high-resolution time in milliseconds relative to an
+   * arbitrary time in the past. It works across different platforms (node.js,
+   * browsers).
+   */
+  now(): number;
+
   /**
    * Encode the provided string into an array of bytes using the provided
    * encoding.

src/platforms/platform_browser.ts

@@ -26,6 +26,14 @@ export class PlatformBrowser implements Platform {
     this.textEncoder = new TextEncoder();
   }
 
+  fetch(path: string, init?: RequestInit): Promise<Response> {
+    return fetch(path, init);
+  }
+
+  now(): number {
+    return performance.now();
+  }
+
   encode(text: string, encoding: string): Uint8Array {
     if (encoding !== 'utf-8' && encoding !== 'utf8') {
       throw new Error(
@@ -36,9 +44,6 @@ export class PlatformBrowser implements Platform {
   decode(bytes: Uint8Array, encoding: string): string {
     return new TextDecoder(encoding).decode(bytes);
   }
-  fetch(path: string, init?: RequestInit): Promise<Response> {
-    return fetch(path, init);
-  }
 }
 
 if (ENV.get('IS_BROWSER')) {

src/platforms/platform_browser_test.ts

@@ -30,6 +30,14 @@ describeWithFlags('PlatformBrowser', BROWSER_ENVS, async () => {
     expect(self.fetch).toHaveBeenCalledWith('test/url', {method: 'GET'});
   });
 
+  it('now should use performance.now', async () => {
+    const platform = new PlatformBrowser();
+
+    const ms = 1234567;
+    spyOn(performance, 'now').and.returnValue(ms);
+    expect(platform.now()).toEqual(ms);
+  });
+
   it('encodeUTF8 single string', () => {
     const platform = new PlatformBrowser();
     const bytes = platform.encode('hello', 'utf-8');

src/platforms/platform_node.ts

@@ -39,6 +39,22 @@ export class PlatformNode implements Platform {
     this.textEncoder = new this.util.TextEncoder();
   }
 
+  fetch(path: string, requestInits?: RequestInit): Promise<Response> {
+    if (ENV.global.fetch != null) {
+      return ENV.global.fetch(path, requestInits);
+    }
+
+    if (systemFetch == null) {
+      systemFetch = getNodeFetch.importFetch();
+    }
+    return systemFetch(path, requestInits);
+  }
+
+  now(): number {
+    const time = process.hrtime();
+    return time[0] * 1000 + time[1] / 1000000;
+  }
+
   encode(text: string, encoding: string): Uint8Array {
     if (encoding !== 'utf-8' && encoding !== 'utf8') {
       throw new Error(
@@ -52,16 +68,6 @@ export class PlatformNode implements Platform {
     }
     return new this.util.TextDecoder(encoding).decode(bytes);
   }
-  fetch(path: string, requestInits?: RequestInit): Promise<Response> {
-    if (ENV.global.fetch != null) {
-      return ENV.global.fetch(path, requestInits);
-    }
-
-    if (systemFetch == null) {
-      systemFetch = getNodeFetch.importFetch();
-    }
-    return systemFetch(path, requestInits);
-  }
 }
 
 if (ENV.get('IS_NODE')) {

src/platforms/platform_node_test.ts

@@ -68,6 +68,12 @@ describeWithFlags('PlatformNode', NODE_ENVS, () => {
     ENV.global.fetch = globalFetch;
   });
 
+  it('now should use process.hrtime', async () => {
+    const time = [100, 200];
+    spyOn(process, 'hrtime').and.returnValue(time);
+    expect(ENV.platform.now()).toEqual(time[0] * 1000 + time[1] / 1000000);
+  });
+
   it('encodeUTF8 single string', () => {
     const platform = new PlatformNode();
     const bytes = platform.encode('hello', 'utf-8');

src/util.ts

@@ -653,16 +653,7 @@ export function makeZerosTypedArray<D extends DataType>(
  */
 /** @doc {heading: 'Util', namespace: 'util'} */
 export function now(): number {
-  if (typeof performance !== 'undefined') {
-    return performance.now();
-  } else if (typeof process !== 'undefined') {
-    const time = process.hrtime();
-    return time[0] * 1000 + time[1] / 1000000;
-  } else {
-    throw new Error(
-        'Cannot measure time in this environment. You should run tf.js ' +
-        'in the browser or in Node.js');
-  }
+  return ENV.platform.now();
 }
 
 export function assertNonNegativeIntegerDimensions(shape: number[]) {