v8  10.1.124 (node 18.2.0)
V8 is Google's open source JavaScript engine
v8-microtask-queue.h
Go to the documentation of this file.
1 // Copyright 2021 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef INCLUDE_V8_MICROTASKS_QUEUE_H_
6 #define INCLUDE_V8_MICROTASKS_QUEUE_H_
7 
8 #include <stddef.h>
9 
10 #include <memory>
11 
12 #include "v8-local-handle.h" // NOLINT(build/include_directory)
13 #include "v8-microtask.h" // NOLINT(build/include_directory)
14 #include "v8config.h" // NOLINT(build/include_directory)
15 
16 namespace v8 {
17 
18 class Function;
19 
20 namespace internal {
21 class Isolate;
22 class MicrotaskQueue;
23 } // namespace internal
24 
25 /**
26  * Represents the microtask queue, where microtasks are stored and processed.
27  * https://html.spec.whatwg.org/multipage/webappapis.html#microtask-queue
28  * https://html.spec.whatwg.org/multipage/webappapis.html#enqueuejob(queuename,-job,-arguments)
29  * https://html.spec.whatwg.org/multipage/webappapis.html#perform-a-microtask-checkpoint
30  *
31  * A MicrotaskQueue instance may be associated to multiple Contexts by passing
32  * it to Context::New(), and they can be detached by Context::DetachGlobal().
33  * The embedder must keep the MicrotaskQueue instance alive until all associated
34  * Contexts are gone or detached.
35  *
36  * Use the same instance of MicrotaskQueue for all Contexts that may access each
37  * other synchronously. E.g. for Web embedding, use the same instance for all
38  * origins that share the same URL scheme and eTLD+1.
39  */
41  public:
42  /**
43  * Creates an empty MicrotaskQueue instance.
44  */
45  static std::unique_ptr<MicrotaskQueue> New(
47 
48  virtual ~MicrotaskQueue() = default;
49 
50  /**
51  * Enqueues the callback to the queue.
52  */
53  virtual void EnqueueMicrotask(Isolate* isolate,
54  Local<Function> microtask) = 0;
55 
56  /**
57  * Enqueues the callback to the queue.
58  */
59  virtual void EnqueueMicrotask(v8::Isolate* isolate,
60  MicrotaskCallback callback,
61  void* data = nullptr) = 0;
62 
63  /**
64  * Adds a callback to notify the embedder after microtasks were run. The
65  * callback is triggered by explicit RunMicrotasks call or automatic
66  * microtasks execution (see Isolate::SetMicrotasksPolicy).
67  *
68  * Callback will trigger even if microtasks were attempted to run,
69  * but the microtasks queue was empty and no single microtask was actually
70  * executed.
71  *
72  * Executing scripts inside the callback will not re-trigger microtasks and
73  * the callback.
74  */
76  MicrotasksCompletedCallbackWithData callback, void* data = nullptr) = 0;
77 
78  /**
79  * Removes callback that was installed by AddMicrotasksCompletedCallback.
80  */
82  MicrotasksCompletedCallbackWithData callback, void* data = nullptr) = 0;
83 
84  /**
85  * Runs microtasks if no microtask is running on this MicrotaskQueue instance.
86  */
87  virtual void PerformCheckpoint(Isolate* isolate) = 0;
88 
89  /**
90  * Returns true if a microtask is running on this MicrotaskQueue instance.
91  */
92  virtual bool IsRunningMicrotasks() const = 0;
93 
94  /**
95  * Returns the current depth of nested MicrotasksScope that has
96  * kRunMicrotasks.
97  */
98  virtual int GetMicrotasksScopeDepth() const = 0;
99 
100  MicrotaskQueue(const MicrotaskQueue&) = delete;
102 
103  private:
104  friend class internal::MicrotaskQueue;
105  MicrotaskQueue() = default;
106 };
107 
108 /**
109  * This scope is used to control microtasks when MicrotasksPolicy::kScoped
110  * is used on Isolate. In this mode every non-primitive call to V8 should be
111  * done inside some MicrotasksScope.
112  * Microtasks are executed when topmost MicrotasksScope marked as kRunMicrotasks
113  * exits.
114  * kDoNotRunMicrotasks should be used to annotate calls not intended to trigger
115  * microtasks.
116  */
118  public:
120 
121  MicrotasksScope(Isolate* isolate, Type type);
122  MicrotasksScope(Isolate* isolate, MicrotaskQueue* microtask_queue, Type type);
124 
125  /**
126  * Runs microtasks if no kRunMicrotasks scope is currently active.
127  */
128  static void PerformCheckpoint(Isolate* isolate);
129 
130  /**
131  * Returns current depth of nested kRunMicrotasks scopes.
132  */
133  static int GetCurrentDepth(Isolate* isolate);
134 
135  /**
136  * Returns true while microtasks are being executed.
137  */
138  static bool IsRunningMicrotasks(Isolate* isolate);
139 
140  // Prevent copying.
143 
144  private:
145  internal::Isolate* const isolate_;
146  internal::MicrotaskQueue* const microtask_queue_;
147  bool run_;
148 };
149 
150 } // namespace v8
151 
152 #endif // INCLUDE_V8_MICROTASKS_QUEUE_H_