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// -*- C++ -*-
//==========================================================================
/**
* @file Semaphore.h
*
* @author Douglas C. Schmidt <d.schmidt@vanderbilt.edu>
*/
//==========================================================================
#ifndef ACE_SEMAPHORE_H
#define ACE_SEMAPHORE_H
#include /**/ "ace/pre.h"
#include /**/ "ace/ACE_export.h"
#if !defined (ACE_LACKS_PRAGMA_ONCE)
# pragma once
#endif /* ACE_LACKS_PRAGMA_ONCE */
#include "ace/OS_NS_Thread.h"
ACE_BEGIN_VERSIONED_NAMESPACE_DECL
class ACE_Time_Value;
/**
* @class ACE_Semaphore
*
* @brief Wrapper for Dijkstra style general semaphores.
*/
class ACE_Export ACE_Semaphore
{
public:
/// Initialize the semaphore, with initial value of "count".
ACE_Semaphore (unsigned int count = 1, // By default make this unlocked.
int type = USYNC_THREAD,
const ACE_TCHAR *name = 0,
void * = 0,
int max = 0x7fffffff);
/// Implicitly destroy the semaphore.
~ACE_Semaphore ();
/**
* Explicitly destroy the semaphore. Note that only one thread
* should call this method since it doesn't protect against race
* conditions.
*/
int remove ();
/// Block the thread until the semaphore count becomes
/// greater than 0, then decrement it.
int acquire ();
/**
* Block the thread until the semaphore count becomes greater than 0
* (at which point it is decremented) or until @a tv times out (in
* which case -1 is returned and @c errno == @c ETIME). Note that @a tv
* is assumed to be in "absolute" rather than "relative" time. The
* value of @a tv is updated upon return to show the actual
* (absolute) acquisition time.
*
* @note Solaris threads do not support timed semaphores.
* Therefore, if you're running on Solaris you might want to
* consider using the ACE POSIX pthreads implementation instead,
* which can be enabled by compiling ACE with
* -DACE_HAS_PTHREADS, rather than -DACE_HAS_STHREADS or
* -DACE_HAS_POSIX_SEM.
*/
int acquire (ACE_Time_Value &tv);
/**
* If @a tv == 0 then call <acquire()> directly. Otherwise, Block
* the thread until the semaphore count becomes greater than 0
* (at which point it is decremented) or until @a tv times out (in
* which case -1 is returned and @c errno == @c ETIME). Note that
* <*tv> is assumed to be in "absolute" rather than "relative" time.
* The value of <*tv> is updated upon return to show the actual
* (absolute) acquisition time.
*
* @note Solaris threads do not support timed semaphores.
* Therefore, if you're running on Solaris you might want to
* consider using the ACE POSIX pthreads implementation instead,
* which can be enabled by compiling ACE with
* -DACE_HAS_PTHREADS, rather than -DACE_HAS_STHREADS or
* -DACE_HAS_POSIX_SEM. */
int acquire (ACE_Time_Value *tv);
/**
* Conditionally decrement the semaphore if count is greater than 0
* (i.e., won't block). Returns -1 on failure. If we "failed"
* because someone else already had the lock, @c errno is set to
* @c EBUSY.
*/
int tryacquire ();
/// Increment the semaphore by 1, potentially unblocking a waiting
/// thread.
int release ();
/// Increment the semaphore by @a release_count, potentially
/// unblocking waiting threads.
int release (unsigned int release_count);
/**
* Acquire semaphore ownership. This calls <acquire> and is only
* here to make the ACE_Semaphore interface consistent with the
* other synchronization APIs.
*/
int acquire_read ();
/**
* Acquire semaphore ownership. This calls <acquire> and is only
* here to make the ACE_Semaphore interface consistent with the
* other synchronization APIs.
*/
int acquire_write ();
/**
* Conditionally acquire semaphore (i.e., won't block). This calls
* <tryacquire> and is only here to make the ACE_Semaphore
* interface consistent with the other synchronization APIs.
* Returns -1 on failure. If we "failed" because someone else
* already had the lock, @c errno is set to @c EBUSY.
*/
int tryacquire_read ();
/**
* Conditionally acquire semaphore (i.e., won't block). This calls
* <tryacquire> and is only here to make the ACE_Semaphore
* interface consistent with the other synchronization APIs.
* Returns -1 on failure. If we "failed" because someone else
* already had the lock, @c errno is set to @c EBUSY.
*/
int tryacquire_write ();
/**
* This is only here to make the ACE_Semaphore
* interface consistent with the other synchronization APIs.
* Assumes the caller has already acquired the semaphore using one of
* the above calls, and returns 0 (success) always.
*/
int tryacquire_write_upgrade ();
/// Dump the state of an object.
void dump () const;
/// Declare the dynamic allocation hooks.
ACE_ALLOC_HOOK_DECLARE;
/// Return the underlying lock.
const ACE_sema_t &lock () const;
protected:
ACE_sema_t semaphore_;
/// Keeps track of whether remove() has been called yet to avoid
/// multiple remove() calls, e.g., explicitly and implicitly in the
/// destructor. This flag isn't protected by a lock, so make sure
/// that you don't have multiple threads simultaneously calling
/// remove () on the same object, which is a bad idea anyway...
bool removed_;
private:
void operator= (const ACE_Semaphore &) = delete;
ACE_Semaphore (const ACE_Semaphore &) = delete;
};
ACE_END_VERSIONED_NAMESPACE_DECL
#if defined (__ACE_INLINE__)
#include "ace/Semaphore.inl"
#endif /* __ACE_INLINE__ */
#include /**/ "ace/post.h"
#endif /* ACE_SEMAPHORE_H */
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