process: add process.cpuUsage() - implementation, doc, tests

Backport to v4.x

Original commit message:
  Add process.cpuUsage() method that returns the user and system
  CPU time usage of the current process

  PR-URL: #6157
  Reviewed-By: Robert Lindstaedt <robert.lindstaedt@gmail.com>
  Reviewed-By: James M Snell <jasnell@gmail.com>
  Reviewed-By: Trevor Norris <trev.norris@gmail.com>
  Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>

PR-URL: #10796
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

doc/api/process.md

@@ -421,6 +421,29 @@ added: v0.7.2
 
 If `process.connected` is false, it is no longer possible to send messages.
 
+## process.cpuUsage([previousValue])
+
+Returns the user and system CPU time usage of the current process, in an object
+with properties `user` and `system`, whose values are microsecond values
+(millionth of a second). These values measure time spent in user and
+system code respectively, and may end up being greater than actual elapsed time
+if multiple CPU cores are performing work for this process.
+
+The result of a previous call to `process.cpuUsage()` can be passed as the
+argument to the function, to get a diff reading.
+
+```js
+const startUsage = process.cpuUsage();
+// { user: 38579, system: 6986 }
+
+// spin the CPU for 500 milliseconds
+const now = Date.now();
+while (Date.now() - now < 500);
+
+console.log(process.cpuUsage(startUsage));
+// { user: 514883, system: 11226 }
+```
+
 ## process.cwd()
 <!-- YAML
 added: v0.1.8

src/node.cc

@@ -102,6 +102,7 @@ using v8::Boolean;
 using v8::Context;
 using v8::EscapableHandleScope;
 using v8::Exception;
+using v8::Float64Array;
 using v8::Function;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -2203,6 +2204,38 @@ void Hrtime(const FunctionCallbackInfo<Value>& args) {
   args.GetReturnValue().Set(tuple);
 }
 
+// Microseconds in a second, as a float, used in CPUUsage() below
+#define MICROS_PER_SEC 1e6
+
+// CPUUsage use libuv's uv_getrusage() this-process resource usage accessor,
+// to access ru_utime (user CPU time used) and ru_stime (system CPU time used),
+// which are uv_timeval_t structs (long tv_sec, long tv_usec).
+// Returns those values as Float64 microseconds in the elements of the array
+// passed to the function.
+void CPUUsage(const FunctionCallbackInfo<Value>& args) {
+  uv_rusage_t rusage;
+
+  // Call libuv to get the values we'll return.
+  int err = uv_getrusage(&rusage);
+  if (err) {
+    // On error, return the strerror version of the error code.
+    Local<String> errmsg = OneByteString(args.GetIsolate(), uv_strerror(err));
+    args.GetReturnValue().Set(errmsg);
+    return;
+  }
+
+  // Get the double array pointer from the Float64Array argument.
+  CHECK(args[0]->IsFloat64Array());
+  Local<Float64Array> array = args[0].As<Float64Array>();
+  CHECK_EQ(array->Length(), 2);
+  Local<ArrayBuffer> ab = array->Buffer();
+  double* fields = static_cast<double*>(ab->GetContents().Data());
+
+  // Set the Float64Array elements to be user / system values in microseconds.
+  fields[0] = MICROS_PER_SEC * rusage.ru_utime.tv_sec + rusage.ru_utime.tv_usec;
+  fields[1] = MICROS_PER_SEC * rusage.ru_stime.tv_sec + rusage.ru_stime.tv_usec;
+}
+
 extern "C" void node_module_register(void* m) {
   struct node_module* mp = reinterpret_cast<struct node_module*>(m);
 
@@ -3153,6 +3186,8 @@ void SetupProcessObject(Environment* env,
 
   env->SetMethod(process, "hrtime", Hrtime);
 
+  env->SetMethod(process, "cpuUsage", CPUUsage);
+
   env->SetMethod(process, "dlopen", DLOpen);
 
   env->SetMethod(process, "uptime", Uptime);

src/node.js

@@ -38,6 +38,7 @@
     startup.processStdio();
     startup.processKillAndExit();
     startup.processSignalHandlers();
+    startup.processCpuUsage();
 
     // Do not initialize channel in debugger agent, it deletes env variable
     // and the main thread won't see it.
@@ -286,6 +287,58 @@
     });
   };
 
+  startup.processCpuUsage = function() {
+    // Get the native function, which will be replaced with a JS version.
+    const _cpuUsage = process.cpuUsage;
+
+    // Create the argument array that will be passed to the native function.
+    const cpuValues = new Float64Array(2);
+
+    // Replace the native function with the JS version that calls the native
+    // function.
+    process.cpuUsage = function cpuUsage(prevValue) {
+      // If a previous value was passed in, ensure it has the correct shape.
+      if (prevValue) {
+        if (!previousValueIsValid(prevValue.user)) {
+          throw new TypeError('value of user property of argument is invalid');
+        }
+
+        if (!previousValueIsValid(prevValue.system)) {
+          throw new TypeError(
+            'value of system property of argument is invalid');
+        }
+      }
+
+      // Call the native function to get the current values.
+      const errmsg = _cpuUsage(cpuValues);
+      if (errmsg) {
+        throw new Error('unable to obtain CPU usage: ' + errmsg);
+      }
+
+      // If a previous value was passed in,
+      // return diff of current from previous.
+      if (prevValue) return {
+        user: cpuValues[0] - prevValue.user,
+        system: cpuValues[1] - prevValue.system
+      };
+
+      // If no previous value passed in, return current value.
+      return {
+        user: cpuValues[0],
+        system: cpuValues[1]
+      };
+
+      // Ensure that a previously passed in value is valid. Currently, the
+      // native implementation always returns
+      // numbers <= Number.MAX_SAFE_INTEGER.
+      function previousValueIsValid(num) {
+        return Number.isFinite(num) &&
+            num <= Number.MAX_SAFE_INTEGER &&
+            num >= 0;
+      }
+    };
+  };
+
   var addPendingUnhandledRejection;
   var hasBeenNotifiedProperty = new WeakMap();
   startup.processNextTick = function() {

test/parallel/test-process-cpuUsage.js

@@ -0,0 +1,67 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+
+const result = process.cpuUsage();
+
+// Validate the result of calling with no previous value argument.
+validateResult(result);
+
+// Validate the result of calling with a previous value argument.
+validateResult(process.cpuUsage(result));
+
+// Ensure the results are >= the previous.
+let thisUsage;
+let lastUsage = process.cpuUsage();
+for (let i = 0; i < 10; i++) {
+  thisUsage = process.cpuUsage();
+  validateResult(thisUsage);
+  assert(thisUsage.user >= lastUsage.user);
+  assert(thisUsage.system >= lastUsage.system);
+  lastUsage = thisUsage;
+}
+
+// Ensure that the diffs are >= 0.
+let startUsage;
+let diffUsage;
+for (let i = 0; i < 10; i++) {
+  startUsage = process.cpuUsage();
+  diffUsage = process.cpuUsage(startUsage);
+  validateResult(startUsage);
+  validateResult(diffUsage);
+  assert(diffUsage.user >= 0);
+  assert(diffUsage.system >= 0);
+}
+
+// Ensure that an invalid shape for the previous value argument throws an error.
+assert.throws(function() { process.cpuUsage(1); });
+assert.throws(function() { process.cpuUsage({}); });
+assert.throws(function() { process.cpuUsage({ user: 'a' }); });
+assert.throws(function() { process.cpuUsage({ system: 'b' }); });
+assert.throws(function() { process.cpuUsage({ user: null, system: 'c' }); });
+assert.throws(function() { process.cpuUsage({ user: 'd', system: null }); });
+assert.throws(function() { process.cpuUsage({ user: -1, system: 2 }); });
+assert.throws(function() { process.cpuUsage({ user: 3, system: -2 }); });
+assert.throws(function() {
+  process.cpuUsage({
+    user: Number.POSITIVE_INFINITY,
+    system: 4
+  });
+});
+assert.throws(function() {
+  process.cpuUsage({
+    user: 5,
+    system: Number.NEGATIVE_INFINITY
+  });
+});
+
+// Ensure that the return value is the expected shape.
+function validateResult(result) {
+  assert.notEqual(result, null);
+
+  assert(Number.isFinite(result.user));
+  assert(Number.isFinite(result.system));
+
+  assert(result.user >= 0);
+  assert(result.system >= 0);
+}

test/pummel/test-process-cpuUsage.js

@@ -0,0 +1,30 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+
+const start = process.cpuUsage();
+
+// Run a busy-loop for specified # of milliseconds.
+const RUN_FOR_MS = 500;
+
+// Define slop factor for checking maximum expected diff values.
+const SLOP_FACTOR = 2;
+
+// Run a busy loop.
+const now = Date.now();
+while (Date.now() - now < RUN_FOR_MS);
+
+// Get a diff reading from when we started.
+const diff = process.cpuUsage(start);
+
+const MICROSECONDS_PER_SECOND = 1000 * 1000;
+
+// Diff usages should be >= 0, <= ~RUN_FOR_MS millis.
+// Let's be generous with the slop factor, defined above, in case other things
+// are happening on this CPU. The <= check may be invalid if the node process
+// is making use of multiple CPUs, in which case, just remove it.
+assert(diff.user >= 0);
+assert(diff.user <= SLOP_FACTOR * RUN_FOR_MS * MICROSECONDS_PER_SECOND);
+
+assert(diff.system >= 0);
+assert(diff.system <= SLOP_FACTOR * RUN_FOR_MS * MICROSECONDS_PER_SECOND);