gears/base/common/mutex.cc

   1 // Copyright 2007, Google Inc.
   2 //
   3 // Redistribution and use in source and binary forms, with or without
   4 // modification, are permitted provided that the following conditions are met:
   5 //
   6 //  1. Redistributions of source code must retain the above copyright notice,
   7 //     this list of conditions and the following disclaimer.
   8 //  2. Redistributions in binary form must reproduce the above copyright notice,
   9 //     this list of conditions and the following disclaimer in the documentation
  10 //     and/or other materials provided with the distribution.
  11 //  3. Neither the name of Google Inc. nor the names of its contributors may be
  12 //     used to endorse or promote products derived from this software without
  13 //     specific prior written permission.
  14 //
  15 // THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
  16 // WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  17 // MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
  18 // EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  19 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  20 // PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
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  24 // ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25
  26 #include <assert.h>
  27 #if BROWSER_IE
  28 #include <windows.h>
  29 #elif BROWSER_FF
  30 #include <gecko_sdk/include/prlock.h>
  31 #elif BROWSER_WEBKIT
  32 #include <pthread.h>
  33 #include <sched.h>
  34 #elif BROWSER_NPAPI
  35 // TODO(mpcomplete): do this right.
  36 #include <windows.h>
  37 #else
  38 #error "BROWSER_xyz not defined."  // centralized check for undefined BROWSER
  39 #endif
  40
  41 #include "gears/base/common/mutex.h"
  42
  43 // TODO(mpcomplete): implement these.
  44 #if BROWSER_NPAPI && defined(WIN32)
  45 #define BROWSER_IE 1
  46 #endif
  47
  48 Mutex::Mutex()
  49 #ifdef DEBUG
  50     : is_locked_(false)
  51 #endif
  52 {
  53 #if BROWSER_IE
  54   InitializeCriticalSection(&crit_sec_);
  55 #elif BROWSER_FF
  56   lock_ = PR_NewLock();
  57 #elif BROWSER_SAFARI
  58   pthread_mutex_init(&mutex_, NULL);
  59 #endif
  60 }
  61
  62
  63 Mutex::~Mutex() {
  64 #if BROWSER_IE
  65   DeleteCriticalSection(&crit_sec_);
  66 #elif BROWSER_FF
  67   if (lock_) PR_DestroyLock(lock_);
  68 #elif BROWSER_SAFARI
  69   pthread_mutex_destroy(&mutex_);
  70 #endif
  71 }
  72
  73
  74 void Mutex::Lock() {
  75 #if BROWSER_IE
  76   EnterCriticalSection(&crit_sec_);
  77 #elif BROWSER_FF
  78   PR_Lock(lock_);
  79 #elif BROWSER_SAFARI
  80   pthread_mutex_lock(&mutex_);
  81 #endif
  82
  83 #ifdef DEBUG
  84   assert(!is_locked_); // Google frowns upon mutex re-entrancy
  85   is_locked_ = true;
  86 #endif
  87 }
  88
  89
  90 void Mutex::Unlock() {
  91 #ifdef DEBUG
  92   assert(is_locked_);
  93   is_locked_ = false;
  94 #endif
  95
  96 #if BROWSER_IE
  97   LeaveCriticalSection(&crit_sec_);
  98 #elif BROWSER_FF
  99   PR_Unlock(lock_);
 100 #elif BROWSER_SAFARI
 101   pthread_mutex_unlock(&mutex_);
 102 #endif
 103 }
 104
 105
 106 void Mutex::Await(const Condition &cond) {
 107   while (!cond.Eval()) {
 108     Unlock();
 109
 110     // Yield the rest of our CPU timeslice before reacquiring the lock.
 111     // Otherwise we'll spin pointlessly here, hurting performance.
 112     // (The Condition cannot possibly change when no other thread runs.)
 113 #if BROWSER_IE
 114     Sleep(0);                       // equivalent to 'yield' in Win32
 115 #elif BROWSER_FF
 116     PR_Sleep(PR_INTERVAL_NO_WAIT);  // equivalent to 'yield' in NSPR
 117 #elif BROWSER_SAFARI
 118     sched_yield();
 119 #endif
 120
 121     Lock();
 122   }
 123 }