1// Copyright 2012 the V8 project authors. All rights reserved.
2// Redistribution and use in source and binary forms, with or without
3// modification, are permitted provided that the following conditions are
4// met:
5//
6//     * Redistributions of source code must retain the above copyright
7//       notice, this list of conditions and the following disclaimer.
8//     * Redistributions in binary form must reproduce the above
9//       copyright notice, this list of conditions and the following
10//       disclaimer in the documentation and/or other materials provided
11//       with the distribution.
12//     * Neither the name of Google Inc. nor the names of its
13//       contributors may be used to endorse or promote products derived
14//       from this software without specific prior written permission.
15//
16// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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25// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27
28#include "once.h"
29
30#ifdef _WIN32
31#include <windows.h>
32#else
33#include <sched.h>
34#endif
35
36#include "atomicops.h"
37#include "checks.h"
38
39namespace v8 {
40namespace internal {
41
42void CallOnceImpl(OnceType* once, PointerArgFunction init_func, void* arg) {
43  AtomicWord state = Acquire_Load(once);
44  // Fast path. The provided function was already executed.
45  if (state == ONCE_STATE_DONE) {
46    return;
47  }
48
49  // The function execution did not complete yet. The once object can be in one
50  // of the two following states:
51  //   - UNINITIALIZED: We are the first thread calling this function.
52  //   - EXECUTING_FUNCTION: Another thread is already executing the function.
53  //
54  // First, try to change the state from UNINITIALIZED to EXECUTING_FUNCTION
55  // atomically.
56  state = Acquire_CompareAndSwap(
57      once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_FUNCTION);
58  if (state == ONCE_STATE_UNINITIALIZED) {
59    // We are the first thread to call this function, so we have to call the
60    // function.
61    init_func(arg);
62    Release_Store(once, ONCE_STATE_DONE);
63  } else {
64    // Another thread has already started executing the function. We need to
65    // wait until it completes the initialization.
66    while (state == ONCE_STATE_EXECUTING_FUNCTION) {
67#ifdef _WIN32
68      ::Sleep(0);
69#else
70      sched_yield();
71#endif
72      state = Acquire_Load(once);
73    }
74  }
75}
76
77} }  // namespace v8::internal
78