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1  /*
2   * Copyright (C) 2007 The Android Open Source Project
3   *
4   * Licensed under the Apache License, Version 2.0 (the "License");
5   * you may not use this file except in compliance with the License.
6   * You may obtain a copy of the License at
7   *
8   *      http://www.apache.org/licenses/LICENSE-2.0
9   *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  #ifndef _LIBS_UTILS_CONDITION_H
18  #define _LIBS_UTILS_CONDITION_H
19  
20  #include <stdint.h>
21  #include <sys/types.h>
22  #include <time.h>
23  
24  #if !defined(_WIN32)
25  # include <pthread.h>
26  #endif
27  
28  #include <utils/Errors.h>
29  #include <utils/Mutex.h>
30  #include <utils/Timers.h>
31  
32  // ---------------------------------------------------------------------------
33  namespace android {
34  // ---------------------------------------------------------------------------
35  
36  /*
37   * Condition variable class.  The implementation is system-dependent.
38   *
39   * Condition variables are paired up with mutexes.  Lock the mutex,
40   * call wait(), then either re-wait() if things aren't quite what you want,
41   * or unlock the mutex and continue.  All threads calling wait() must
42   * use the same mutex for a given Condition.
43   */
44  class Condition {
45  public:
46      enum {
47          PRIVATE = 0,
48          SHARED = 1
49      };
50  
51      enum WakeUpType {
52          WAKE_UP_ONE = 0,
53          WAKE_UP_ALL = 1
54      };
55  
56      Condition();
57      Condition(int type);
58      ~Condition();
59      // Wait on the condition variable.  Lock the mutex before calling.
60      status_t wait(Mutex& mutex);
61      // same with relative timeout
62      status_t waitRelative(Mutex& mutex, nsecs_t reltime);
63      // Signal the condition variable, allowing exactly one thread to continue.
64      void signal();
65      // Signal the condition variable, allowing one or all threads to continue.
signal(WakeUpType type)66      void signal(WakeUpType type) {
67          if (type == WAKE_UP_ONE) {
68              signal();
69          } else {
70              broadcast();
71          }
72      }
73      // Signal the condition variable, allowing all threads to continue.
74      void broadcast();
75  
76  private:
77  #if !defined(_WIN32)
78      pthread_cond_t mCond;
79  #else
80      void*   mState;
81  #endif
82  };
83  
84  // ---------------------------------------------------------------------------
85  
86  #if !defined(_WIN32)
87  
Condition()88  inline Condition::Condition() {
89      pthread_cond_init(&mCond, NULL);
90  }
Condition(int type)91  inline Condition::Condition(int type) {
92      if (type == SHARED) {
93          pthread_condattr_t attr;
94          pthread_condattr_init(&attr);
95          pthread_condattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
96          pthread_cond_init(&mCond, &attr);
97          pthread_condattr_destroy(&attr);
98      } else {
99          pthread_cond_init(&mCond, NULL);
100      }
101  }
~Condition()102  inline Condition::~Condition() {
103      pthread_cond_destroy(&mCond);
104  }
wait(Mutex & mutex)105  inline status_t Condition::wait(Mutex& mutex) {
106      return -pthread_cond_wait(&mCond, &mutex.mMutex);
107  }
waitRelative(Mutex & mutex,nsecs_t reltime)108  inline status_t Condition::waitRelative(Mutex& mutex, nsecs_t reltime) {
109  #if defined(HAVE_PTHREAD_COND_TIMEDWAIT_RELATIVE)
110      struct timespec ts;
111      ts.tv_sec  = reltime/1000000000;
112      ts.tv_nsec = reltime%1000000000;
113      return -pthread_cond_timedwait_relative_np(&mCond, &mutex.mMutex, &ts);
114  #else // HAVE_PTHREAD_COND_TIMEDWAIT_RELATIVE
115      struct timespec ts;
116  #if defined(__linux__)
117      clock_gettime(CLOCK_REALTIME, &ts);
118  #else // __APPLE__
119      // we don't support the clocks here.
120      struct timeval t;
121      gettimeofday(&t, NULL);
122      ts.tv_sec = t.tv_sec;
123      ts.tv_nsec= t.tv_usec*1000;
124  #endif
125      ts.tv_sec += reltime/1000000000;
126      ts.tv_nsec+= reltime%1000000000;
127      if (ts.tv_nsec >= 1000000000) {
128          ts.tv_nsec -= 1000000000;
129          ts.tv_sec  += 1;
130      }
131      return -pthread_cond_timedwait(&mCond, &mutex.mMutex, &ts);
132  #endif // HAVE_PTHREAD_COND_TIMEDWAIT_RELATIVE
133  }
signal()134  inline void Condition::signal() {
135      /*
136       * POSIX says pthread_cond_signal wakes up "one or more" waiting threads.
137       * However bionic follows the glibc guarantee which wakes up "exactly one"
138       * waiting thread.
139       *
140       * man 3 pthread_cond_signal
141       *   pthread_cond_signal restarts one of the threads that are waiting on
142       *   the condition variable cond. If no threads are waiting on cond,
143       *   nothing happens. If several threads are waiting on cond, exactly one
144       *   is restarted, but it is not specified which.
145       */
146      pthread_cond_signal(&mCond);
147  }
broadcast()148  inline void Condition::broadcast() {
149      pthread_cond_broadcast(&mCond);
150  }
151  
152  #endif // !defined(_WIN32)
153  
154  // ---------------------------------------------------------------------------
155  }; // namespace android
156  // ---------------------------------------------------------------------------
157  
158  #endif // _LIBS_UTILS_CONDITON_H
159