thread_semaphore.h

多线程库

#ifndef __THREADS_SEMAPHORE_H
#define __THREADS_SEMAPHORE_H

#include <thread_attributes.h>
#include <thread_spinlock.h>

class wait_queue;

/**
 * A semaphore, it functions in much a similar way as a mutex
 * does, but with some exceptions.
 *
 * @author Orn E. Hansen <[e-mail]>
 * @short Implements a semaphore, for thread synchronisation.
 */
class semaphore {
 protected:
  static char *s_project;
  int s_id;
  wait_queue *s_waiting;
  attributes::scope s_scope;
  struct storage {
    int s_magic;
    spinlock s_sync;
    int s_count;
  } *_s;
 public:
  semaphore(attributes::scope);
  semaphore(attributes::scope, int);
  semaphore();
  semaphore(int);
  ~semaphore();

  /**
   * Increment the semaphore count, the top most blocking thread on
   * the waiting list is restarted.
   *
   * @return The updated value, of the semaphore count.
   */
  int post();
  /**
   * Block the calling process, until the semaphore count becomes
   * greater than 1, then atomically decrement it.
   * 
   * @return The current count of the semaphore.
   */
  int wait();
  /**
   * Decrement the count, if it is greater than zero.  This is a
   * non-blocking call.
   *
   * @return The count of the semaphore after decrement, or -1 not.
   */
  int trywait();
  /**
   * The shared memory scheme, wants a single name to identify the
   * overall program.  It is possible, and perhaps desired that
   * part cond/mutex/semaphore have their own name identification
   * tree.  This is possible, by stating that it should be branch
   * of the main file name, with a give extension.
   *
   * <pre>
   * main()
   * {
   *   semaphore *sv;
   *
   *   pthread::set_project( "my_project" );
   *   semaphore::project_par( "sem" );
   *   sv = new semaphore(attributes::process_shared);
   *   ...
   * }
   * </pre>
   *
   * This will set the project to my_project, and all semaphores
   * will be derived from my_project_sem.
   *
   * @param part A C string containing the semaphore part name.
   */
  static void project_part(const char *);
};

#endif /* __THREADS_SEMAPHORE_H */