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/System/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;
  27 RWMutexImpl::RWMutexImpl() { }
  28 RWMutexImpl::~RWMutexImpl() { }
  29 bool RWMutexImpl::reader_acquire() { return true; }
  30 bool RWMutexImpl::reader_release() { return true; }
  31 bool RWMutexImpl::writer_acquire() { return true; }
  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
  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     pthread_rwlockattr_t attr;
  75
  76     // Initialize the rwlock attributes
  77     int errorcode = pthread_rwlockattr_init(&attr);
  78     assert(errorcode == 0);
  79
  80 #if !defined(__FreeBSD__) && !defined(__OpenBSD__) && !defined(__NetBSD__) && !defined(__DragonFly__)
  81     // Make it a process local rwlock
  82     errorcode = pthread_rwlockattr_setpshared(&attr, PTHREAD_PROCESS_PRIVATE);
  83 #endif
  84
  85     // Initialize the rwlock
  86     errorcode = pthread_rwlock_init(rwlock, &attr);
  87     assert(errorcode == 0);
  88
  89     // Destroy the attributes
  90     errorcode = pthread_rwlockattr_destroy(&attr);
  91     assert(errorcode == 0);
  92
  93     // Assign the data member
  94     data_ = rwlock;
  95   }
  96 }
  97
  98 // Destruct a RWMutex
  99 RWMutexImpl::~RWMutexImpl()
 100 {
 101   if (pthread_enabled)
 102   {
 103     pthread_rwlock_t* rwlock = static_cast<pthread_rwlock_t*>(data_);
 104     assert(rwlock != 0);
 105     pthread_rwlock_destroy(rwlock);
 106     free(rwlock);
 107   }
 108 }
 109
 110 bool
 111 RWMutexImpl::reader_acquire()
 112 {
 113   if (pthread_enabled)
 114   {
 115     pthread_rwlock_t* rwlock = static_cast<pthread_rwlock_t*>(data_);
 116     assert(rwlock != 0);
 117
 118     int errorcode = pthread_rwlock_rdlock(rwlock);
 119     return errorcode == 0;
 120   }
 121   return false;
 122 }
 123
 124 bool
 125 RWMutexImpl::reader_release()
 126 {
 127   if (pthread_enabled)
 128   {
 129     pthread_rwlock_t* rwlock = static_cast<pthread_rwlock_t*>(data_);
 130     assert(rwlock != 0);
 131
 132     int errorcode = pthread_rwlock_unlock(rwlock);
 133     return errorcode == 0;
 134   }
 135   return false;
 136 }
 137
 138 bool
 139 RWMutexImpl::writer_acquire()
 140 {
 141   if (pthread_enabled)
 142   {
 143     pthread_rwlock_t* rwlock = static_cast<pthread_rwlock_t*>(data_);
 144     assert(rwlock != 0);
 145
 146     int errorcode = pthread_rwlock_wrlock(rwlock);
 147     return errorcode == 0;
 148   }
 149   return false;
 150 }
 151
 152 bool
 153 RWMutexImpl::writer_release()
 154 {
 155   if (pthread_enabled)
 156   {
 157     pthread_rwlock_t* rwlock = static_cast<pthread_rwlock_t*>(data_);
 158     assert(rwlock != 0);
 159
 160     int errorcode = pthread_rwlock_unlock(rwlock);
 161     return errorcode == 0;
 162   }
 163   return false;
 164 }
 165
 166 }
 167
 168 #elif defined(LLVM_ON_UNIX)
 169 #include "Unix/RWMutex.inc"
 170 #elif defined( LLVM_ON_WIN32)
 171 #include "Win32/RWMutex.inc"
 172 #else
 173 #warning Neither LLVM_ON_UNIX nor LLVM_ON_WIN32 was set in System/Mutex.cpp
 174 #endif
 175 #endif