lib/System/RWMutex.cpp

   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/Compiler.h"
  16 #include "llvm/System/RWMutex.h"
  17 #include <cstring>
  18
  19 //===----------------------------------------------------------------------===//
  20 //=== WARNING: Implementation here must contain only TRULY operating system
  21 //===          independent code.
  22 //===----------------------------------------------------------------------===//
  23
  24 #if !defined(ENABLE_THREADS) || ENABLE_THREADS == 0
  25 // Define all methods as no-ops if threading is explicitly disabled
  26 namespace llvm {
  27 using namespace sys;
  28 RWMutexImpl::RWMutexImpl() { }
  29 RWMutexImpl::~RWMutexImpl() { }
  30 bool RWMutexImpl::reader_acquire() { return true; }
  31 bool RWMutexImpl::reader_release() { return true; }
  32 bool RWMutexImpl::writer_acquire() { return true; }
  33 bool RWMutexImpl::writer_release() { return true; }
  34 }
  35 #else
  36
  37 #if defined(HAVE_PTHREAD_H) && defined(HAVE_PTHREAD_RWLOCK_INIT)
  38
  39 #include <cassert>
  40 #include <pthread.h>
  41 #include <stdlib.h>
  42
  43 namespace llvm {
  44 using namespace sys;
  45
  46
  47 // This variable is useful for situations where the pthread library has been
  48 // compiled with weak linkage for its interface symbols. This allows the
  49 // threading support to be turned off by simply not linking against -lpthread.
  50 // In that situation, the value of pthread_mutex_init will be 0 and
  51 // consequently pthread_enabled will be false. In such situations, all the
  52 // pthread operations become no-ops and the functions all return false. If
  53 // pthread_rwlock_init does have an address, then rwlock support is enabled.
  54 // Note: all LLVM tools will link against -lpthread if its available since it
  55 //       is configured into the LIBS variable.
  56 // Note: this line of code generates a warning if pthread_rwlock_init is not
  57 //       declared with weak linkage. It's safe to ignore the warning.
  58 static const bool pthread_enabled = true;
  59
  60 // Construct a RWMutex using pthread calls
  61 RWMutexImpl::RWMutexImpl()
  62   : data_(0)
  63 {
  64   if (pthread_enabled)
  65   {
  66     // Declare the pthread_rwlock data structures
  67     pthread_rwlock_t* rwlock =
  68       static_cast<pthread_rwlock_t*>(malloc(sizeof(pthread_rwlock_t)));
  69
  70 #ifdef __APPLE__
  71     // Workaround a bug/mis-feature in Darwin's pthread_rwlock_init.
  72     bzero(rwlock, sizeof(pthread_rwlock_t));
  73 #endif
  74
  75     // Initialize the rwlock
  76     int ATTRIBUTE_UNUSED errorcode = pthread_rwlock_init(rwlock, NULL);
  77     assert(errorcode == 0);
  78
  79     // Assign the data member
  80     data_ = rwlock;
  81   }
  82 }
  83
  84 // Destruct a RWMutex
  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
  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
 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
 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
 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 "Win32/RWMutex.inc"
 154 #else
 155 #warning Neither LLVM_ON_UNIX nor LLVM_ON_WIN32 was set in System/Mutex.cpp
 156 #endif
 157 #endif