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
24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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
39 namespace v8 {
40 namespace internal {
41
CallOnceImpl(OnceType * once,PointerArgFunction init_func,void * arg)42 void 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