async_hooks: initial async_hooks implementation

Fill this commit messsage with more details about the change once all
changes are rebased.

* Add lib/async_hooks.js

* Add JS methods to AsyncWrap for handling the async id stack

* Introduce AsyncReset() so that JS functions can reset the id and again
  trigger the init hooks, allow AsyncWrap::Reset() to be called from JS
  via asyncReset().

* Add env variable to test additional things in test/common.js

PR-URL: https://github.com/nodejs/node/pull/12892
Ref: https://github.com/nodejs/node/pull/11883
Ref: https://github.com/nodejs/node/pull/8531
Reviewed-By: Andreas Madsen <amwebdk@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

2 files changed, 492 insertions, 4 deletions

diff --git a/lib/async_hooks.js b/lib/async_hooks.js
new file mode 100644
index 0000000000..736b189097
--- /dev/null
+++ b/lib/async_hooks.js
@@ -0,0 +1,488 @@
+'use strict';
+
+const async_wrap = process.binding('async_wrap');
+/* Both these arrays are used to communicate between JS and C++ with as little
+ * overhead as possible.
+ *
+ * async_hook_fields is a Uint32Array() that communicates the number of each
+ * type of active hooks of each type and wraps the uin32_t array of
+ * node::Environment::AsyncHooks::fields_.
+ *
+ * async_uid_fields is a Float64Array() that contains the async/trigger ids for
+ * several operations. These fields are as follows:
+ *   kCurrentAsyncId: The async id of the current execution stack.
+ *   kCurrentTriggerId: The trigger id of the current execution stack.
+ *   kAsyncUidCntr: Counter that tracks the unique ids given to new resources.
+ *   kInitTriggerId: Written to just before creating a new resource, so the
+ *    constructor knows what other resource is responsible for its init().
+ *    Used this way so the trigger id doesn't need to be passed to every
+ *    resource's constructor.
+ */
+const { async_hook_fields, async_uid_fields } = async_wrap;
+// Used to change the state of the async id stack.
+const { pushAsyncIds, popAsyncIds } = async_wrap;
+// Array of all AsyncHooks that will be iterated whenever an async event fires.
+// Using var instead of (preferably const) in order to assign
+// tmp_active_hooks_array if a hook is enabled/disabled during hook execution.
+var active_hooks_array = [];
+// Track whether a hook callback is currently being processed. Used to make
+// sure active_hooks_array isn't altered in mid execution if another hook is
+// added or removed.
+var processing_hook = false;
+// Use to temporarily store and updated active_hooks_array if the user enables
+// or disables a hook while hooks are being processed.
+var tmp_active_hooks_array = null;
+// Keep track of the field counds held in tmp_active_hooks_array.
+var tmp_async_hook_fields = null;
+
+// Each constant tracks how many callbacks there are for any given step of
+// async execution. These are tracked so if the user didn't include callbacks
+// for a given step, that step can bail out early.
+const { kInit, kBefore, kAfter, kDestroy, kCurrentAsyncId, kCurrentTriggerId,
+    kAsyncUidCntr, kInitTriggerId } = async_wrap.constants;
+
+// Used in AsyncHook and AsyncEvent.
+const async_id_symbol = Symbol('_asyncId');
+const trigger_id_symbol = Symbol('_triggerId');
+const init_symbol = Symbol('init');
+const before_symbol = Symbol('before');
+const after_symbol = Symbol('after');
+const destroy_symbol = Symbol('destroy');
+
+// Setup the callbacks that node::AsyncWrap will call when there are hooks to
+// process. They use the same functions as the JS embedder API.
+async_wrap.setupHooks({ init,
+                        before: emitBeforeN,
+                        after: emitAfterN,
+                        destroy: emitDestroyN });
+
+// Used to fatally abort the process if a callback throws.
+function fatalError(e) {
+  if (typeof e.stack === 'string') {
+    process._rawDebug(e.stack);
+  } else {
+    const o = { message: e };
+    Error.captureStackTrace(o, fatalError);
+    process._rawDebug(o.stack);
+  }
+  if (process.execArgv.some(
+      (e) => /^--abort[_-]on[_-]uncaught[_-]exception$/.test(e))) {
+    process.abort();
+  }
+  process.exit(1);
+}
+
+
+// Public API //
+
+class AsyncHook {
+  constructor({ init, before, after, destroy }) {
+    if (init && typeof init !== 'function')
+      throw new TypeError('init must be a function');
+    if (before && typeof before !== 'function')
+      throw new TypeError('before must be a function');
+    if (after && typeof after !== 'function')
+      throw new TypeError('after must be a function');
+    if (destroy && typeof destroy !== 'function')
+      throw new TypeError('destroy must be a function');
+
+    this[init_symbol] = init;
+    this[before_symbol] = before;
+    this[after_symbol] = after;
+    this[destroy_symbol] = destroy;
+  }
+
+  enable() {
+    // The set of callbacks for a hook should be the same regardless of whether
+    // enable()/disable() are run during their execution. The following
+    // references are reassigned to the tmp arrays if a hook is currently being
+    // processed.
+    const [hooks_array, hook_fields] = getHookArrays();
+
+    // Each hook is only allowed to be added once.
+    if (hooks_array.includes(this))
+      return;
+
+    // createHook() has already enforced that the callbacks are all functions,
+    // so here simply increment the count of whether each callbacks exists or
+    // not.
+    hook_fields[kInit] += +!!this[init_symbol];
+    hook_fields[kBefore] += +!!this[before_symbol];
+    hook_fields[kAfter] += +!!this[after_symbol];
+    hook_fields[kDestroy] += +!!this[destroy_symbol];
+    hooks_array.push(this);
+    return this;
+  }
+
+  disable() {
+    const [hooks_array, hook_fields] = getHookArrays();
+
+    const index = hooks_array.indexOf(this);
+    if (index === -1)
+      return;
+
+    hook_fields[kInit] -= +!!this[init_symbol];
+    hook_fields[kBefore] -= +!!this[before_symbol];
+    hook_fields[kAfter] -= +!!this[after_symbol];
+    hook_fields[kDestroy] -= +!!this[destroy_symbol];
+    hooks_array.splice(index, 1);
+    return this;
+  }
+}
+
+
+function getHookArrays() {
+  if (!processing_hook)
+    return [active_hooks_array, async_hook_fields];
+  // If this hook is being enabled while in the middle of processing the array
+  // of currently active hooks then duplicate the current set of active hooks
+  // and store this there. This shouldn't fire until the next time hooks are
+  // processed.
+  if (tmp_active_hooks_array === null)
+    storeActiveHooks();
+  return [tmp_active_hooks_array, tmp_async_hook_fields];
+}
+
+
+function storeActiveHooks() {
+  tmp_active_hooks_array = active_hooks_array.slice();
+  // Don't want to make the assumption that kInit to kDestroy are indexes 0 to
+  // 4. So do this the long way.
+  tmp_async_hook_fields = [];
+  tmp_async_hook_fields[kInit] = async_hook_fields[kInit];
+  tmp_async_hook_fields[kBefore] = async_hook_fields[kBefore];
+  tmp_async_hook_fields[kAfter] = async_hook_fields[kAfter];
+  tmp_async_hook_fields[kDestroy] = async_hook_fields[kDestroy];
+}
+
+
+// Then restore the correct hooks array in case any hooks were added/removed
+// during hook callback execution.
+function restoreTmpHooks() {
+  active_hooks_array = tmp_active_hooks_array;
+  async_hook_fields[kInit] = tmp_async_hook_fields[kInit];
+  async_hook_fields[kBefore] = tmp_async_hook_fields[kBefore];
+  async_hook_fields[kAfter] = tmp_async_hook_fields[kAfter];
+  async_hook_fields[kDestroy] = tmp_async_hook_fields[kDestroy];
+
+  tmp_active_hooks_array = null;
+  tmp_async_hook_fields = null;
+}
+
+
+function createHook(fns) {
+  return new AsyncHook(fns);
+}
+
+
+function currentId() {
+  return async_uid_fields[kCurrentAsyncId];
+}
+
+
+function triggerId() {
+  return async_uid_fields[kCurrentTriggerId];
+}
+
+
+// Embedder API //
+
+class AsyncEvent {
+  constructor(type, triggerId) {
+    this[async_id_symbol] = ++async_uid_fields[kAsyncUidCntr];
+    // Read and reset the current kInitTriggerId so that when the constructor
+    // finishes the kInitTriggerId field is always 0.
+    if (triggerId === undefined) {
+      triggerId = initTriggerId();
+    // If a triggerId was passed, any kInitTriggerId still must be null'd.
+    } else {
+      async_uid_fields[kInitTriggerId] = 0;
+    }
+    this[trigger_id_symbol] = triggerId;
+
+    // Return immediately if there's nothing to do.
+    if (async_hook_fields[kInit] === 0)
+      return;
+
+    if (typeof type !== 'string' || type.length <= 0)
+      throw new TypeError('type must be a string with length > 0');
+    if (!Number.isSafeInteger(triggerId) || triggerId < 0)
+      throw new RangeError('triggerId must be an unsigned integer');
+
+    processing_hook = true;
+    for (var i = 0; i < active_hooks_array.length; i++) {
+      if (typeof active_hooks_array[i][init_symbol] === 'function') {
+        runInitCallback(active_hooks_array[i][init_symbol],
+                        this[async_id_symbol],
+                        type,
+                        triggerId,
+                        this);
+      }
+    }
+    processing_hook = false;
+  }
+
+  emitBefore() {
+    emitBeforeS(this[async_id_symbol], this[trigger_id_symbol]);
+    return this;
+  }
+
+  emitAfter() {
+    emitAfterS(this[async_id_symbol]);
+    return this;
+  }
+
+  emitDestroy() {
+    emitDestroyS(this[async_id_symbol]);
+    return this;
+  }
+
+  asyncId() {
+    return this[async_id_symbol];
+  }
+
+  triggerId() {
+    return this[trigger_id_symbol];
+  }
+}
+
+
+function runInAsyncIdScope(asyncId, cb) {
+  // Store the async id now to make sure the stack is still good when the ids
+  // are popped off the stack.
+  const prevId = currentId();
+  pushAsyncIds(asyncId, prevId);
+  try {
+    cb();
+  } finally {
+    popAsyncIds(asyncId);
+  }
+}
+
+
+// Sensitive Embedder API //
+
+// Increment the internal id counter and return the value. Important that the
+// counter increment first. Since it's done the same way in
+// Environment::new_async_uid()
+function newUid() {
+  return ++async_uid_fields[kAsyncUidCntr];
+}
+
+
+// Return the triggerId meant for the constructor calling it. It's up to the
+// user to safeguard this call and make sure it's zero'd out when the
+// constructor is complete.
+function initTriggerId() {
+  var tId = async_uid_fields[kInitTriggerId];
+  // Reset value after it's been called so the next constructor doesn't
+  // inherit it by accident.
+  async_uid_fields[kInitTriggerId] = 0;
+  if (tId <= 0)
+    tId = async_uid_fields[kCurrentAsyncId];
+  return tId;
+}
+
+
+function setInitTriggerId(triggerId) {
+  // CHECK(Number.isSafeInteger(triggerId))
+  // CHECK(triggerId > 0)
+  async_uid_fields[kInitTriggerId] = triggerId;
+}
+
+
+function emitInitS(asyncId, type, triggerId, resource) {
+  // Short circuit all checks for the common case. Which is that no hooks have
+  // been set. Do this to remove performance impact for embedders (and core).
+  // Even though it bypasses all the argument checks. The performance savings
+  // here is critical.
+  if (async_hook_fields[kInit] === 0)
+    return;
+
+  // This can run after the early return check b/c running this function
+  // manually means that the embedder must have used initTriggerId().
+  if (!Number.isSafeInteger(triggerId)) {
+    if (triggerId !== undefined)
+      resource = triggerId;
+    triggerId = initTriggerId();
+  }
+
+  // I'd prefer allowing these checks to not exist, or only throw in a debug
+  // build, in order to improve performance.
+  if (!Number.isSafeInteger(asyncId) || asyncId < 0)
+    throw new RangeError('asyncId must be an unsigned integer');
+  if (typeof type !== 'string' || type.length <= 0)
+    throw new TypeError('type must be a string with length > 0');
+  if (!Number.isSafeInteger(triggerId) || triggerId < 0)
+    throw new RangeError('triggerId must be an unsigned integer');
+
+  processing_hook = true;
+  for (var i = 0; i < active_hooks_array.length; i++) {
+    if (typeof active_hooks_array[i][init_symbol] === 'function') {
+      runInitCallback(
+        active_hooks_array[i][init_symbol], asyncId, type, triggerId, resource);
+    }
+  }
+  processing_hook = false;
+
+  // Isn't null if hooks were added/removed while the hooks were running.
+  if (tmp_active_hooks_array !== null) {
+    restoreTmpHooks();
+  }
+}
+
+
+function emitBeforeN(asyncId) {
+  processing_hook = true;
+  for (var i = 0; i < active_hooks_array.length; i++) {
+    if (typeof active_hooks_array[i][before_symbol] === 'function') {
+      runCallback(active_hooks_array[i][before_symbol], asyncId);
+    }
+  }
+  processing_hook = false;
+
+  if (tmp_active_hooks_array !== null) {
+    restoreTmpHooks();
+  }
+}
+
+
+// Usage: emitBeforeS(asyncId[, triggerId]). If triggerId is omitted then
+// asyncId will be used instead.
+function emitBeforeS(asyncId, triggerId = asyncId) {
+  // CHECK(Number.isSafeInteger(asyncId) && asyncId > 0)
+  // CHECK(Number.isSafeInteger(triggerId) && triggerId > 0)
+
+  // Validate the ids.
+  if (asyncId < 0 || triggerId < 0) {
+    fatalError('before(): asyncId or triggerId is less than zero ' +
+               `(asyncId: ${asyncId}, triggerId: ${triggerId})`);
+  }
+
+  pushAsyncIds(asyncId, triggerId);
+
+  if (async_hook_fields[kBefore] === 0) {
+    return;
+  }
+
+  emitBeforeN(asyncId);
+}
+
+
+// Called from native. The asyncId stack handling is taken care of there before
+// this is called.
+function emitAfterN(asyncId) {
+  if (async_hook_fields[kAfter] > 0) {
+    processing_hook = true;
+    for (var i = 0; i < active_hooks_array.length; i++) {
+      if (typeof active_hooks_array[i][after_symbol] === 'function') {
+        runCallback(active_hooks_array[i][after_symbol], asyncId);
+      }
+    }
+    processing_hook = false;
+  }
+
+  if (tmp_active_hooks_array !== null) {
+    restoreTmpHooks();
+  }
+}
+
+
+// TODO(trevnorris): Calling emitBefore/emitAfter from native can't adjust the
+// kIdStackIndex. But what happens if the user doesn't have both before and
+// after callbacks.
+function emitAfterS(asyncId) {
+  emitAfterN(asyncId);
+  popAsyncIds(asyncId);
+}
+
+
+function emitDestroyS(asyncId) {
+  // Return early if there are no destroy callbacks, or on attempt to emit
+  // destroy on the void.
+  if (async_hook_fields[kDestroy] === 0 || asyncId === 0)
+    return;
+  async_wrap.addIdToDestroyList(asyncId);
+}
+
+
+function emitDestroyN(asyncId) {
+  processing_hook = true;
+  for (var i = 0; i < active_hooks_array.length; i++) {
+    if (typeof active_hooks_array[i][destroy_symbol] === 'function') {
+      runCallback(active_hooks_array[i][destroy_symbol], asyncId);
+    }
+  }
+  processing_hook = false;
+
+  if (tmp_active_hooks_array !== null) {
+    restoreTmpHooks();
+  }
+}
+
+
+// Emit callbacks for native calls. Since some state can be setup directly from
+// C++ there's no need to perform all the work here.
+
+// This should only be called if hooks_array has kInit > 0. There are no global
+// values to setup. Though hooks_array will be cloned if C++ needed to call
+// init().
+// TODO(trevnorris): Perhaps have MakeCallback call a single JS function that
+// does the before/callback/after calls to remove two additional calls to JS.
+function init(asyncId, type, resource, triggerId) {
+  processing_hook = true;
+  for (var i = 0; i < active_hooks_array.length; i++) {
+    if (typeof active_hooks_array[i][init_symbol] === 'function') {
+      runInitCallback(
+        active_hooks_array[i][init_symbol], asyncId, type, triggerId, resource);
+    }
+  }
+  processing_hook = false;
+}
+
+
+// Generalized callers for all callbacks that handles error handling.
+
+// If either runInitCallback() or runCallback() throw then force the
+// application to shutdown if one of the callbacks throws. This may change in
+// the future depending on whether it can be determined if there's a slim
+// chance of the application remaining stable after handling one of these
+// exceptions.
+
+function runInitCallback(cb, asyncId, type, triggerId, resource) {
+  try {
+    cb(asyncId, type, triggerId, resource);
+  } catch (e) {
+    fatalError(e);
+  }
+}
+
+
+function runCallback(cb, asyncId) {
+  try {
+    cb(asyncId);
+  } catch (e) {
+    fatalError(e);
+  }
+}
+
+
+// Placing all exports down here because the exported classes won't export
+// otherwise.
+module.exports = {
+  // Public API
+  createHook,
+  currentId,
+  triggerId,
+  // Embedder API
+  AsyncEvent,
+  runInAsyncIdScope,
+  // Sensitive Embedder API
+  newUid,
+  initTriggerId,
+  setInitTriggerId,
+  emitInit: emitInitS,
+  emitBefore: emitBeforeS,
+  emitAfter: emitAfterS,
+  emitDestroy: emitDestroyS,
+};
diff --git a/lib/internal/module.js b/lib/internal/module.js
index 49bd9b84ee..08d8f770c8 100644
--- a/lib/internal/module.js
+++ b/lib/internal/module.js
@@ -77,10 +77,10 @@ function stripShebang(content) {
 }
 
 const builtinLibs = [
-  'assert', 'buffer', 'child_process', 'cluster', 'crypto', 'dgram', 'dns',
-  'domain', 'events', 'fs', 'http', 'https', 'net', 'os', 'path', 'punycode',
-  'querystring', 'readline', 'repl', 'stream', 'string_decoder', 'tls', 'tty',
-  'url', 'util', 'v8', 'vm', 'zlib'
+  'assert', 'async_hooks', 'buffer', 'child_process', 'cluster', 'crypto',
+  'dgram', 'dns', 'domain', 'events', 'fs', 'http', 'https', 'net', 'os',
+  'path', 'punycode', 'querystring', 'readline', 'repl', 'stream',
+  'string_decoder', 'tls', 'tty', 'url', 'util', 'v8', 'vm', 'zlib'
 ];
 
 function addBuiltinLibsToObject(object) {