JMutex.hh

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#ifndef __JLANG__JMUTEX__
#define __JLANG__JMUTEX__

#include <pthread.h>

/**
 * \file
 * Very basic lock facilities to be used in multithreaded programs.
 * \author cpellegrino
 */

namespace JSYNCHRONIZATION {}
namespace JPP { using namespace JSYNCHRONIZATION; }

namespace JSYNCHRONIZATION {

/**
 * Scoped lock.
 *
 * The main purpose of this class is to provide an exception-safe locking
 * facility.
 * The lock on the mutex is acquired during construction, while the
 * unlock is performed in the destructor.
 *
 * Es:
 * Case 1, without scoped lock:
 * using namespace JSYNCHRONIZATION;
 * JMutex mutex;
 *
 * {
 *   mutex.lock();
 *   throwing_function(variable_to_protect); // <- this shall throw
 *   mutex.lock();                           // <- this call is never
 *                                           // executed -> deadlock
 * }
 *
 * Case 2, with scoped lock:
 * using namespace JSYNCHRONIZATION;
 * JMutex mutex;
 *
 * {
 *   JScopedLock(mutex);
 *   throwing_function(variable_to_protect); // <- this shall throw
 * } // the lock is released here automatically
 */
template<typename Lockable>
class JBasicScopedLock
{
  Lockable* m_lock;

  /**
   * Neither copy-constructible nor copy-assignable
   */
  JBasicScopedLock(const JBasicScopedLock&);
  JBasicScopedLock operator =(const JBasicScopedLock&);

 public:

  /**
   * Constructor
   *  \param  lock     a lockable object (e.g. JScopedLock)
   */
  explicit JBasicScopedLock(Lockable& lock)
    :
    m_lock(&lock)
  {
    m_lock->lock();
  }

  /**
   * Destructor
   */
  ~JBasicScopedLock()
  {
    unlock();
  }

  /**
   * Unlock the mutex.
   * \return    0 on success, an error code otherwise.
   *            See man 3p pthread_mutex_lock for further info.
   */
  int unlock()
  {
    return m_lock->unlock();
  }
};

/**
 * Mutex.
 */
class JMutex
{
  pthread_mutex_t m_mutex;

 public:

  /**
   * Constructor.
   */
  JMutex()
  {
    pthread_mutex_init(&m_mutex, 0);
  }

  /**
   * Destructor.
   */
  ~JMutex()
  {
    pthread_mutex_destroy(&m_mutex);
  }

  /**
   * Lock the mutex.
   * \return    0 on success, an error code otherwise.
   *            See man 3p pthread_mutex_lock for further info.
   */
  int lock()
  {
    return pthread_mutex_lock(&m_mutex);
  }

  /**
   * Try lock the mutex.
   * \return    0 on success, an error code otherwise.
   *            See man 3p pthread_mutex_lock for further info.
   */
  int try_lock()
  {
    return pthread_mutex_trylock(&m_mutex);
  }

  /**
   * Unlock the mutex.
   * \return    0 on success, an error code otherwise.
   *            See man 3p pthread_mutex_lock for further info.
   */
  int unlock()
  {
    return pthread_mutex_unlock(&m_mutex);
  }

  typedef JBasicScopedLock<JMutex> JScopedLock;
};

} // ns JSYNCHRONIZATION

#endif // __JLANG__JMUTEX__