1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
|
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef mozilla_dom_workers_jsexecutionmanager_h__
#define mozilla_dom_workers_jsexecutionmanager_h__
#include <stdint.h>
#include <deque>
#include "MainThreadUtils.h"
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/CondVar.h"
#include "mozilla/Mutex.h"
#include "mozilla/RefPtr.h"
#include "nsISupports.h"
class nsIGlobalObject;
namespace mozilla {
class ErrorResult;
namespace dom {
class WorkerPrivate;
// The code in this file is responsible for throttling JS execution. It does
// this by introducing a JSExecutionManager class. An execution manager may be
// applied to any number of worker threads or a DocGroup on the main thread.
//
// JS environments associated with a JS execution manager may only execute on a
// certain amount of CPU cores in parallel.
//
// Whenever the main thread, or a worker thread begins executing JS it should
// make sure AutoRequestJSThreadExecution is present on the stack, in practice
// this is done by it being part of AutoEntryScript.
//
// Whenever the main thread may end up blocking on the activity of a worker
// thread, it should make sure to have an AutoYieldJSThreadExecution object
// on the stack.
//
// Whenever a worker thread may end up blocking on the main thread or the
// activity of another worker thread, it should make sure to have an
// AutoYieldJSThreadExecution object on the stack.
//
// Failure to do this may result in a deadlock. When a deadlock occurs due
// to these circumstances we will crash after 20 seconds.
//
// For the main thread this class should only be used in the case of an
// emergency surrounding exploitability of SharedArrayBuffers. A single
// execution manager will then be shared between all Workers and the main
// thread doc group containing the SharedArrayBuffer and ensure all this code
// only runs in a serialized manner. On the main thread we therefore may have
// 1 execution manager per DocGroup, as this is the granularity at which
// SharedArrayBuffers may be present.
class AutoRequestJSThreadExecution;
class AutoYieldJSThreadExecution;
// This class is used to regulate JS execution when for whatever reason we wish
// to throttle execution of multiple JS environments to occur with a certain
// maximum of synchronously executing threads. This should be used through
// the stack helper classes.
class JSExecutionManager {
public:
NS_INLINE_DECL_THREADSAFE_REFCOUNTING(JSExecutionManager)
explicit JSExecutionManager(int32_t aMaxRunning = 1)
: mMaxRunning(aMaxRunning) {}
enum class RequestState { Granted, ExecutingAlready };
static void Initialize();
static void Shutdown();
static JSExecutionManager* GetSABSerializationManager();
private:
friend class AutoRequestJSThreadExecution;
friend class AutoYieldJSThreadExecution;
~JSExecutionManager() = default;
// Methods used by Auto*JSThreadExecution
// Request execution permission, returns ExecutingAlready if execution was
// already granted or does not apply to this thread.
RequestState RequestJSThreadExecution();
// Yield JS execution, this asserts that permission is actually granted.
void YieldJSThreadExecution();
// Yield JS execution if permission was granted. This returns false if no
// permission is granted. This method is needed because an execution manager
// may have been set in between the ctor and dtor of
// AutoYieldJSThreadExecution.
bool YieldJSThreadExecutionIfGranted();
RequestState RequestJSThreadExecutionMainThread();
// Execution manager currently managing the main thread.
// MainThread access only.
static JSExecutionManager* mCurrentMTManager;
// Workers waiting to be given permission for execution.
// Guarded by mExecutionQueueMutex.
std::deque<WorkerPrivate*> mExecutionQueue
MOZ_GUARDED_BY(mExecutionQueueMutex);
// Number of threads currently executing concurrently for this manager.
// Guarded by mExecutionQueueMutex.
int32_t mRunning MOZ_GUARDED_BY(mExecutionQueueMutex) = 0;
// Number of threads allowed to run concurrently for environments managed
// by this manager.
// Guarded by mExecutionQueueMutex.
int32_t mMaxRunning MOZ_GUARDED_BY(mExecutionQueueMutex) = 1;
// Mutex that guards the execution queue and associated state.
Mutex mExecutionQueueMutex =
Mutex{"JSExecutionManager::sExecutionQueueMutex"};
// ConditionVariables that blocked threads wait for.
CondVar mExecutionQueueCondVar =
CondVar{mExecutionQueueMutex, "JSExecutionManager::sExecutionQueueMutex"};
// Whether the main thread is currently executing for this manager.
// MainThread access only.
bool mMainThreadIsExecuting = false;
// Whether the main thread is currently awaiting permission to execute. Main
// thread execution is always prioritized.
// Guarded by mExecutionQueueMutex.
bool mMainThreadAwaitingExecution MOZ_GUARDED_BY(mExecutionQueueMutex) =
false;
};
// Helper for managing execution requests and allowing re-entrant permission
// requests.
class MOZ_STACK_CLASS AutoRequestJSThreadExecution {
public:
explicit AutoRequestJSThreadExecution(nsIGlobalObject* aGlobalObject,
bool aIsMainThread);
~AutoRequestJSThreadExecution() {
if (mExecutionGrantingManager) {
mExecutionGrantingManager->YieldJSThreadExecution();
}
if (mIsMainThread) {
if (mOldGrantingManager) {
mOldGrantingManager->RequestJSThreadExecution();
}
JSExecutionManager::mCurrentMTManager = mOldGrantingManager;
}
}
private:
// The manager we obtained permission from. nullptr if permission was already
// granted.
RefPtr<JSExecutionManager> mExecutionGrantingManager;
// The manager we had permission from before, and where permission should be
// re-requested upon destruction.
RefPtr<JSExecutionManager> mOldGrantingManager;
// We store this for performance reasons.
bool mIsMainThread;
};
// Class used to wrap code which essentially exits JS execution and may block
// on other threads.
class MOZ_STACK_CLASS AutoYieldJSThreadExecution {
public:
AutoYieldJSThreadExecution();
~AutoYieldJSThreadExecution() {
if (mExecutionGrantingManager) {
mExecutionGrantingManager->RequestJSThreadExecution();
if (NS_IsMainThread()) {
JSExecutionManager::mCurrentMTManager = mExecutionGrantingManager;
}
}
}
private:
// Set to the granting manager if we were granted permission here.
RefPtr<JSExecutionManager> mExecutionGrantingManager;
};
} // namespace dom
} // namespace mozilla
#endif // mozilla_dom_workers_jsexecutionmanager_h__
|
