benchmark: new options setup and teardown

This commit introduces two new options to the Benchmark tool: setup
and teardown. The setup option runs before any forks are created,
and teardown executes after all forks have completed.

Author: 0hmX

benchmark/common.js

@@ -9,6 +9,8 @@ function allow() {
 
 class Benchmark {
   constructor(fn, configs, options = {}) {
+    this.setup = options.setup;
+    this.teardown = options.teardown;
     // Used to make sure a benchmark only start a timer once
     this._started = false;
 
@@ -62,6 +64,9 @@ class Benchmark {
       if (process.env.NODE_RUN_BENCHMARK_FN !== undefined) {
         fn(this.config);
       } else {
+        if (this.setup) {
+          this.setup();
+        }
         // _run will use fork() to create a new process for each configuration
         // combination.
         this._run();
@@ -234,6 +239,8 @@ class Benchmark {
 
         if (queueIndex + 1 < this.queue.length) {
           recursive(queueIndex + 1);
+        } else if (this.globalTeardown) {
+          this.teardown();
         }
       });
     };

doc/contributing/writing-and-running-benchmarks.md

@@ -523,6 +523,14 @@ The arguments of `createBenchmark` are:
   Each configuration is a property with an array of possible values.
   The configuration values can only be strings or numbers.
 * `options` {Object} The benchmark options. Supported options:
+  * `setup` {Function} A function to be run once by the main "controller"
+    process before any benchmark child processes are spawned. Ideal for
+    preparing the environment for the entire benchmark suite.
+
+  * `teardown` {Function} A function to be run once by the main "controller"
+    process after all benchmark child processes have completed. Ideal for
+    cleaning up the environment.
+
   * `flags` {Array} Contains node-specific command line flags to pass to
     the child process.
 
@@ -585,6 +593,13 @@ const configs = {
 const options = {
   // Add --expose-internals in order to require internal modules in main
   flags: ['--zero-fill-buffers'],
+  // Setup and teardown functions are run in the parent process, once.
+  setup() {
+    console.log('Running global setup.');
+  },
+  teardown() {
+    console.log('Running global teardown.');
+  },
 };
 
 // `main` and `configs` are required, `options` is optional.