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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;
     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     // 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
     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 "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