Fix memory leak around global.process

Summary: This memory leak was discovered in #584 and has always been present in jest. It likely affects the runtime performance of jest on low-memory machines *a lot* and we don't notice it much on devservers. I will tag and release 0.7.0 with this fix (because 0.7.0 also removes a bunch of APIs, see the changelog, it cannot be a patch release).

Two samples from before and after:

* P20276376 (150 mb vs 47 mb on 34 Relay tests)
* P20276601 (54 mb vs 38 mb flat on the functional tests)

I also added a way to pretty print the output (see the second paste). By adding `--logHeapUsage` to jest it adds these statistics after every test run. When node's global `gc` function is exposed, it calls it beforehand to make sure we are logging accurate data. I am going to think about whether it makes sense to expose this more easily (adding `--runInBand` etc. is slightly confusing) if I am confident it isn't bad for performance. On automated test runs you might want to log this and be able to log the final memory usage to whatever logging system you use to be able to track memory usage of test runs (and applications) over time.

Note: It is time we rewrite jest's configs *completely*. I have plans for this and it is a discussion for a separate diff. For now I have to copy-pasta some code to make everything work in the internal and external runners and tack on the argv data to the config objects.

public

Reviewed By: DmitrySoshnikov

Differential Revision: D2608363

fb-gh-sync-id: ab3bda143c22ef06e2e1b32a4c92d8ad0a2151cb

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## 0.7.0
 
+* Fixed a memory leak with test contexts. Jest now properly cleans up
+  test environments after each test. Added `--logHeapUsage` to log memory
+  usage after each test. Note: this is option is meant for debugging memory
+  leaks and might significantly slow down your test run.
 * Removed `mock-modules`, `node-haste` and `mocks` virtual modules. This is a
   breaking change of undocumented public API. Usage of this API can safely be
   automatically updated through an automated codemod:

bin/jest.js

@@ -165,6 +165,13 @@ const argv = optimist
       ),
       type: 'boolean',
     },
+    logHeapUsage: {
+      description: _wrapDesc(
+        'Logs the heap usage after every test. Useful to debug memory ' +
+        'leaks. Use together with `--runInBand` and `--expose-gc` in node.'
+      ),
+      type: 'boolean',
+    },
   })
   .check(function(argv) {
     if (argv.runInBand && argv.hasOwnProperty('maxWorkers')) {

src/DefaultTestReporter.js

@@ -49,16 +49,25 @@ class DefaultTestReporter {
       ? (testResult.perfStats.end - testResult.perfStats.start) / 1000
       : null;
 
-    let testRunTimeString;
+    let testDetail = [];
     if (testRunTime !== null) {
-      testRunTimeString = '(' + testRunTime + 's)';
-      if (testRunTime > 2.5) {
-        testRunTimeString = this._formatMsg(testRunTimeString, FAIL_COLOR);
-      }
+      testDetail.push(
+        testRunTime > 2.5
+          ? this._formatMsg(testRunTime + 's', FAIL_COLOR)
+          : testRunTime + 's'
+      );
+    }
+
+    if (testResult.memoryUsage) {
+      const toMB = bytes => Math.floor(bytes / 1024 / 1024);
+      testDetail.push(
+        `${toMB(testResult.memoryUsage)} MB current`,
+        `${toMB(testResult.maxMemoryUsage)} MB max`
+      );
     }
 
     const resultHeader = this._getResultHeader(allTestsPassed, pathStr, [
-      testRunTimeString,
+      (testDetail.length ? '(' + testDetail.join(', ') + ')' : null),
     ]);
 
     /*

src/JSDomEnvironment.js

@@ -26,7 +26,9 @@ class JSDomEnvironment {
 
     // Forward some APIs
     this.global.Buffer = Buffer;
-    this.global.process = process;
+    // `this.global.process` is mutated in FakeTimers. Make a copy of the
+    // object for the jsdom environment to prevent memory leaks.
+    this.global.process = Object.assign({}, process);
     this.global.setImmediate = setImmediate;
     this.global.clearImmediate = clearImmediate;
 

src/TestRunner.js

@@ -70,13 +70,14 @@ function optionPathToRegex(p) {
  * @param options See DEFAULT_OPTIONS for descriptions on the various options
  *                and their defaults.
  */
-
 class TestRunner {
 
   constructor(config, options) {
     this._config = config;
     this._configDeps = null;
     this._moduleLoaderResourceMap = null;
+    // Maximum memory usage if `logHeapUsage` is enabled.
+    this._maxMemoryUsage = 0;
     this._testPathDirsRegExp = new RegExp(
       config.testPathDirs
         .map(dir => optionPathToRegex(dir))
@@ -91,6 +92,7 @@ class TestRunner {
           .join('|') +
       ')$'
     );
+
     // Map from testFilePath -> time it takes to run the test. Used to
     // optimally schedule bigger test runs.
     this._testPerformanceCache = null;
@@ -375,22 +377,27 @@ class TestRunner {
 
       const testExecStats = {start: Date.now()};
       return testRunner(config, env, moduleLoader, testFilePath)
-        .then(results => {
+        .then(result => {
           testExecStats.end = Date.now();
 
-          results.perfStats = testExecStats;
-          results.testFilePath = testFilePath;
-          results.coverage =
+          result.perfStats = testExecStats;
+          result.testFilePath = testFilePath;
+          result.coverage =
             config.collectCoverage
             ? moduleLoader.getAllCoverageInfo()
             : {};
 
-          return results;
+          return result;
         });
     }).then(
-      results => Promise.resolve().then(() => {
+      result => Promise.resolve().then(() => {
         env.dispose();
-        return results;
+
+        if (config.logHeapUsage) {
+          this._addMemoryUsage(result);
+        }
+
+        return result;
       }),
       err => Promise.resolve().then(() => {
         env.dispose();
@@ -483,12 +490,10 @@ class TestRunner {
       const TestReporter = require(config.testReporter);
       if (config.useStderr) {
         /* eslint-disable fb-www/object-create-only-one-param */
-        reporter = new TestReporter(
-          Object.create(
-            process,
-            { stdout: { value: process.stderr } }
-          )
-        );
+        reporter = new TestReporter(Object.create(
+          process,
+          {stdout: {value: process.stderr}}
+        ));
         /* eslint-enable fb-www/object-create-only-one-param */
       } else {
         reporter = new TestReporter();
@@ -563,19 +568,15 @@ class TestRunner {
       .then(this._cacheTestResults.bind(this));
   }
 
-  _createTestRun(
-    testPaths, onTestResult, onRunFailure
-  ) {
+  _createTestRun(testPaths, onTestResult, onRunFailure) {
     if (this._opts.runInBand || testPaths.length <= 1) {
       return this._createInBandTestRun(testPaths, onTestResult, onRunFailure);
     } else {
       return this._createParallelTestRun(testPaths, onTestResult, onRunFailure);
     }
   }
 
-  _createInBandTestRun(
-    testPaths, onTestResult, onRunFailure
-  ) {
+  _createInBandTestRun(testPaths, onTestResult, onRunFailure) {
     let testSequence = Promise.resolve();
     testPaths.forEach(testPath =>
       testSequence = testSequence
@@ -617,6 +618,16 @@ class TestRunner {
           })
       ))).then(() => workerFarm.end(farm));
   }
+
+  _addMemoryUsage(result) {
+    if (global.gc) {
+      global.gc();
+    }
+    const memoryUsage = process.memoryUsage().heapUsed;
+    this._maxMemoryUsage = Math.max(this._maxMemoryUsage, memoryUsage);
+    result.maxMemoryUsage = this._maxMemoryUsage;
+    result.memoryUsage = memoryUsage;
+  }
 }
 
 function _pathStreamToPromise(stream) {

src/jest.js

@@ -109,6 +109,10 @@ function _promiseConfig(argv, packageRoot) {
       config.useStderr = true;
     }
 
+    if (argv.logHeapUsage) {
+      config.logHeapUsage = argv.logHeapUsage;
+    }
+
     config.noStackTrace = argv.noStackTrace;
 
     return config;

src/lib/utils.js

@@ -261,6 +261,7 @@ function normalizeConfig(config) {
       case 'moduleFileExtensions':
       case 'noHighlight':
       case 'noStackTrace':
+      case 'logHeapUsage':
       case 'cache':
       case 'verbose':
         value = config[key];