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1 //===- RWMutex.cpp - Reader/Writer Mutual Exclusion Lock --------*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the llvm::sys::RWMutex class.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Config/config.h"
15 #include "llvm/Support/RWMutex.h"
16 #include <cstring>
17 
18 //===----------------------------------------------------------------------===//
19 //=== WARNING: Implementation here must contain only TRULY operating system
20 //===          independent code.
21 //===----------------------------------------------------------------------===//
22 
23 #if !defined(ENABLE_THREADS) || ENABLE_THREADS == 0
24 // Define all methods as no-ops if threading is explicitly disabled
25 namespace llvm {
26 using namespace sys;
RWMutexImpl()27 RWMutexImpl::RWMutexImpl() { }
~RWMutexImpl()28 RWMutexImpl::~RWMutexImpl() { }
reader_acquire()29 bool RWMutexImpl::reader_acquire() { return true; }
reader_release()30 bool RWMutexImpl::reader_release() { return true; }
writer_acquire()31 bool RWMutexImpl::writer_acquire() { return true; }
writer_release()32 bool RWMutexImpl::writer_release() { return true; }
33 }
34 #else
35 
36 #if defined(HAVE_PTHREAD_H) && defined(HAVE_PTHREAD_RWLOCK_INIT)
37 
38 #include <cassert>
39 #include <pthread.h>
40 #include <stdlib.h>
41 
42 namespace llvm {
43 using namespace sys;
44 
45 
46 // This variable is useful for situations where the pthread library has been
47 // compiled with weak linkage for its interface symbols. This allows the
48 // threading support to be turned off by simply not linking against -lpthread.
49 // In that situation, the value of pthread_mutex_init will be 0 and
50 // consequently pthread_enabled will be false. In such situations, all the
51 // pthread operations become no-ops and the functions all return false. If
52 // pthread_rwlock_init does have an address, then rwlock support is enabled.
53 // Note: all LLVM tools will link against -lpthread if its available since it
54 //       is configured into the LIBS variable.
55 // Note: this line of code generates a warning if pthread_rwlock_init is not
56 //       declared with weak linkage. It's safe to ignore the warning.
57 static const bool pthread_enabled = true;
58 
59 // Construct a RWMutex using pthread calls
RWMutexImpl()60 RWMutexImpl::RWMutexImpl()
61   : data_(0)
62 {
63   if (pthread_enabled)
64   {
65     // Declare the pthread_rwlock data structures
66     pthread_rwlock_t* rwlock =
67       static_cast<pthread_rwlock_t*>(malloc(sizeof(pthread_rwlock_t)));
68 
69 #ifdef __APPLE__
70     // Workaround a bug/mis-feature in Darwin's pthread_rwlock_init.
71     bzero(rwlock, sizeof(pthread_rwlock_t));
72 #endif
73 
74     // Initialize the rwlock
75     int errorcode = pthread_rwlock_init(rwlock, NULL);
76     (void)errorcode;
77     assert(errorcode == 0);
78 
79     // Assign the data member
80     data_ = rwlock;
81   }
82 }
83 
84 // Destruct a RWMutex
~RWMutexImpl()85 RWMutexImpl::~RWMutexImpl()
86 {
87   if (pthread_enabled)
88   {
89     pthread_rwlock_t* rwlock = static_cast<pthread_rwlock_t*>(data_);
90     assert(rwlock != 0);
91     pthread_rwlock_destroy(rwlock);
92     free(rwlock);
93   }
94 }
95 
96 bool
reader_acquire()97 RWMutexImpl::reader_acquire()
98 {
99   if (pthread_enabled)
100   {
101     pthread_rwlock_t* rwlock = static_cast<pthread_rwlock_t*>(data_);
102     assert(rwlock != 0);
103 
104     int errorcode = pthread_rwlock_rdlock(rwlock);
105     return errorcode == 0;
106   } else return false;
107 }
108 
109 bool
reader_release()110 RWMutexImpl::reader_release()
111 {
112   if (pthread_enabled)
113   {
114     pthread_rwlock_t* rwlock = static_cast<pthread_rwlock_t*>(data_);
115     assert(rwlock != 0);
116 
117     int errorcode = pthread_rwlock_unlock(rwlock);
118     return errorcode == 0;
119   } else return false;
120 }
121 
122 bool
writer_acquire()123 RWMutexImpl::writer_acquire()
124 {
125   if (pthread_enabled)
126   {
127     pthread_rwlock_t* rwlock = static_cast<pthread_rwlock_t*>(data_);
128     assert(rwlock != 0);
129 
130     int errorcode = pthread_rwlock_wrlock(rwlock);
131     return errorcode == 0;
132   } else return false;
133 }
134 
135 bool
writer_release()136 RWMutexImpl::writer_release()
137 {
138   if (pthread_enabled)
139   {
140     pthread_rwlock_t* rwlock = static_cast<pthread_rwlock_t*>(data_);
141     assert(rwlock != 0);
142 
143     int errorcode = pthread_rwlock_unlock(rwlock);
144     return errorcode == 0;
145   } else return false;
146 }
147 
148 }
149 
150 #elif defined(LLVM_ON_UNIX)
151 #include "Unix/RWMutex.inc"
152 #elif defined( LLVM_ON_WIN32)
153 #include "Windows/RWMutex.inc"
154 #else
155 #warning Neither LLVM_ON_UNIX nor LLVM_ON_WIN32 was set in System/Mutex.cpp
156 #endif
157 #endif
158