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1 : // Protocol Buffers - Google's data interchange format
2 : // Copyright 2008 Google Inc. All rights reserved.
3 : // https://developers.google.com/protocol-buffers/
4 : //
5 : // Redistribution and use in source and binary forms, with or without
6 : // modification, are permitted provided that the following conditions are
7 : // met:
8 : //
9 : // * Redistributions of source code must retain the above copyright
10 : // notice, this list of conditions and the following disclaimer.
11 : // * Redistributions in binary form must reproduce the above
12 : // copyright notice, this list of conditions and the following disclaimer
13 : // in the documentation and/or other materials provided with the
14 : // distribution.
15 : // * Neither the name of Google Inc. nor the names of its
16 : // contributors may be used to endorse or promote products derived from
17 : // this software without specific prior written permission.
18 : //
19 : // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20 : // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
21 : // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
22 : // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
23 : // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
24 : // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
25 : // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
26 : // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
27 : // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
28 : // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
29 : // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30 :
31 : // Author: kenton@google.com (Kenton Varda)
32 : //
33 : // emulates google3/base/once.h
34 : //
35 : // This header is intended to be included only by internal .cc files and
36 : // generated .pb.cc files. Users should not use this directly.
37 :
38 : #include <google/protobuf/stubs/once.h>
39 :
40 : #ifndef GOOGLE_PROTOBUF_NO_THREAD_SAFETY
41 :
42 : #ifdef _WIN32
43 : #include <windows.h>
44 : #else
45 : #include <sched.h>
46 : #endif
47 :
48 : #include <google/protobuf/stubs/atomicops.h>
49 :
50 : namespace google {
51 : namespace protobuf {
52 :
53 : namespace {
54 :
55 : void SchedYield() {
56 : #ifdef _WIN32
57 : Sleep(0);
58 : #else // POSIX
59 0 : sched_yield();
60 : #endif
61 : }
62 :
63 : } // namespace
64 :
65 190 : void GoogleOnceInitImpl(ProtobufOnceType* once, Closure* closure) {
66 190 : internal::AtomicWord state = internal::Acquire_Load(once);
67 : // Fast path. The provided closure was already executed.
68 190 : if (state == ONCE_STATE_DONE) {
69 190 : return;
70 : }
71 : // The closure execution did not complete yet. The once object can be in one
72 : // of the two following states:
73 : // - UNINITIALIZED: We are the first thread calling this function.
74 : // - EXECUTING_CLOSURE: Another thread is already executing the closure.
75 : //
76 : // First, try to change the state from UNINITIALIZED to EXECUTING_CLOSURE
77 : // atomically.
78 : state = internal::Acquire_CompareAndSwap(
79 190 : once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_CLOSURE);
80 190 : if (state == ONCE_STATE_UNINITIALIZED) {
81 : // We are the first thread to call this function, so we have to call the
82 : // closure.
83 190 : closure->Run();
84 : internal::Release_Store(once, ONCE_STATE_DONE);
85 : } else {
86 : // Another thread has already started executing the closure. We need to
87 : // wait until it completes the initialization.
88 0 : while (state == ONCE_STATE_EXECUTING_CLOSURE) {
89 : // Note that futex() could be used here on Linux as an improvement.
90 : SchedYield();
91 0 : state = internal::Acquire_Load(once);
92 : }
93 : }
94 : }
95 :
96 : } // namespace protobuf
97 : } // namespace google
98 :
99 : #endif // GOOGLE_PROTOBUF_NO_THREAD_SAFETY
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