src/posix/Monitor.cxx

/*
 * Copyright (c) 2005, Eric Crahen
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is furnished
 * to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 */

#include "Monitor.h"
#include "../Debug.h"
#include "../TimeStrategy.h"

#include <errno.h>
#include <assert.h>
#include <signal.h>

namespace ZThread {

Monitor::Monitor() : _owner(0), _waiting(false) {

  pthread_cond_init(&_waitCond, 0);
  pthread_mutex_init(&_waitLock, 0);

}

Monitor::~Monitor() {

  assert(!_waiting);

  pthread_cond_destroy(&_waitCond);
  pthread_mutex_destroy(&_waitLock);

}

Monitor::STATE Monitor::wait(unsigned long ms) {

  // Update the owner on first use. The owner will not change, each
  // thread waits only on a single Monitor and a Monitor is never
  // shared
  if(_owner == 0)
    _owner = pthread_self();

  STATE state(INVALID);

  // Serialize access to the state of the Monitor
  // and test the state to determine if a wait is needed.

  pthread_mutex_lock(&_waitLock);

  if(pending(ANYTHING)) {

    // Return without waiting when possible
    state = next();

    pthread_mutex_unlock(&_waitLock);
    return state;

  }

  // Unlock the external lock if a wait() is probably needed.
  // Access to the state is still serial.
  _lock.release();

  // Wait for a transition in the state that is of interest, this
  // allows waits to exclude certain flags (e.g. INTERRUPTED)
  // for a single wait() w/o actually discarding those flags -
  // they will remain set until a wait interested in those flags
  // occurs.
  //  if(!currentState(interest)) {

  // Wait, ignoring signals
  _waiting = true;
  int status = 0;

  if(ms == 0) { // Wait forever

    do { // ignore signals unless the state is interesting
      status = pthread_cond_wait(&_waitCond, &_waitLock);
    } while(status == EINTR && !pending(ANYTHING));

    // Akwaken only when a state is pending
    assert(status == 0);

  } else {

    // Find the target time
    TimeStrategy t;

    ms += t.milliseconds();

    unsigned long s = t.seconds() + (ms / 1000);
    ms %= 1000;

    // Convert to a timespec
    struct ::timespec timeout;

    timeout.tv_sec = s;
    timeout.tv_nsec = ms*1000000;

    // Wait ignoring signals until the state is interesting
    do {

      // When a timeout occurs, update the state to reflect that.
      status = pthread_cond_timedwait(&_waitCond, &_waitLock, &timeout);

    } while(status == EINTR && !pending(ANYTHING));

    // Akwaken only when a state is pending or when the timeout expired
    assert(status == 0 || status == ETIMEDOUT);

    if(status == ETIMEDOUT)
      push(TIMEDOUT);

  }

  // Get the next available STATE
  state = next();
  _waiting = false;

  pthread_mutex_unlock(&_waitLock);

  // Reaquire the external lock, keep from deadlocking threads calling
  // notify(), interrupt(), etc.

  _lock.acquire();

  return state;

}


bool Monitor::interrupt() {

  // Serialize access to the state
  pthread_mutex_lock(&_waitLock);

  bool wasInterruptable = !pending(INTERRUPTED);
  bool hadWaiter = _waiting;

  if(wasInterruptable) {

    // Update the state & wake the waiter if there is one
    push(INTERRUPTED);

    wasInterruptable = false;

    if(hadWaiter && !masked(Monitor::INTERRUPTED))
      pthread_cond_signal(&_waitCond);
    else
      wasInterruptable = !pthread_equal(_owner, pthread_self());

  }

  pthread_mutex_unlock(&_waitLock);

  // Only returns true when an interrupted thread is not currently blocked
  return wasInterruptable;

}

bool Monitor::isInterrupted() {

  // Serialize access to the state
  pthread_mutex_lock(&_waitLock);

  bool wasInterrupted = pending(INTERRUPTED);

  clear(INTERRUPTED);

  pthread_mutex_unlock(&_waitLock);

  return wasInterrupted;

}

bool Monitor::isCanceled() {

  // Serialize access to the state
  pthread_mutex_lock(&_waitLock);

  bool wasCanceled = examine(CANCELED);

  if(pthread_equal(_owner, pthread_self()))
    clear(INTERRUPTED);

  pthread_mutex_unlock(&_waitLock);

  return wasCanceled;

}

bool Monitor::cancel() {

  // Serialize access to the state
  pthread_mutex_lock(&_waitLock);

  bool wasInterrupted = !pending(INTERRUPTED);
  bool hadWaiter = _waiting;

  push(CANCELED);

  if(wasInterrupted) {

    // Update the state & wake the waiter if there is one
    push(INTERRUPTED);

    if(hadWaiter && !masked(Monitor::INTERRUPTED))
      pthread_cond_signal(&_waitCond);

  }

  pthread_mutex_unlock(&_waitLock);

  return wasInterrupted;

}

bool Monitor::notify() {

  // Serialize access to the state
  pthread_mutex_lock(&_waitLock);

  bool wasNotifyable = !pending(INTERRUPTED);

  if(wasNotifyable) {

    // Set the flag and wake the waiter if there
    // is one
    push(SIGNALED);

    if(_waiting)
      pthread_cond_signal(&_waitCond);

  }

  pthread_mutex_unlock(&_waitLock);

  return wasNotifyable;

}

} // namespace ZThread