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
SchedYield()55 void SchedYield() {
56 #ifdef _WIN32
57 Sleep(0);
58 #else // POSIX
59 sched_yield();
60 #endif
61 }
62
63 } // namespace
64
GoogleOnceInitImpl(ProtobufOnceType * once,Closure * closure)65 void GoogleOnceInitImpl(ProtobufOnceType* once, Closure* closure) {
66 internal::AtomicWord state = internal::Acquire_Load(once);
67 // Fast path. The provided closure was already executed.
68 if (state == ONCE_STATE_DONE) {
69 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 once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_CLOSURE);
80 if (state == ONCE_STATE_UNINITIALIZED) {
81 // We are the first thread to call this function, so we have to call the
82 // closure.
83 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 while (state == ONCE_STATE_EXECUTING_CLOSURE) {
89 // Note that futex() could be used here on Linux as an improvement.
90 SchedYield();
91 state = internal::Acquire_Load(once);
92 }
93 }
94 }
95
96 } // namespace protobuf
97 } // namespace google
98
99 #endif // GOOGLE_PROTOBUF_NO_THREAD_SAFETY
100