IlmThreadSemaphore.h

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//
// SPDX-License-Identifier: BSD-3-Clause
// Copyright (c) Contributors to the OpenEXR Project.
//

#ifndef INCLUDED_ILM_THREAD_SEMAPHORE_H
#define INCLUDED_ILM_THREAD_SEMAPHORE_H

//-----------------------------------------------------------------------------
//
//      class Semaphore -- a wrapper class for
//      system-dependent counting semaphores
//
//-----------------------------------------------------------------------------

#include "IlmThreadExport.h"

#include "IlmThreadConfig.h"
#include "IlmThreadNamespace.h"

#if ILMTHREAD_THREADING_ENABLED
#   if ILMTHREAD_HAVE_POSIX_SEMAPHORES
#      include <semaphore.h>
#   elif defined(__APPLE__)
#      include <dispatch/dispatch.h>
#   elif (defined (_WIN32) || defined (_WIN64))
#      ifdef NOMINMAX
#         undef NOMINMAX
#      endif
#      define NOMINMAX
#      include <windows.h>
#   else
#      include <mutex>
#      include <condition_variable>
#   endif
#endif

ILMTHREAD_INTERNAL_NAMESPACE_HEADER_ENTER


class ILMTHREAD_EXPORT_TYPE Semaphore
{
  public:

    ILMTHREAD_EXPORT Semaphore (unsigned int value = 0);
    ILMTHREAD_EXPORT virtual ~Semaphore();

    ILMTHREAD_EXPORT void wait();
    ILMTHREAD_EXPORT bool tryWait();
    ILMTHREAD_EXPORT void post();
    ILMTHREAD_EXPORT int  value() const;

  private:

#if ILMTHREAD_HAVE_POSIX_SEMAPHORES

        mutable sem_t _semaphore;

#elif defined(__APPLE__)
        mutable dispatch_semaphore_t _semaphore;

#elif (defined (_WIN32) || defined (_WIN64))

        mutable HANDLE _semaphore;

#elif ILMTHREAD_THREADING_ENABLED
        //
        // If the platform has threads but no semapohores,
        // then we implement them ourselves using condition variables
        //

        struct sema_t
        {
            unsigned int count;
            unsigned long numWaiting;
        std::mutex mutex;
        std::condition_variable nonZero;
        };

        mutable sema_t _semaphore;
  
#endif

    void operator = (const Semaphore& s) = delete;
    Semaphore (const Semaphore& s) = delete;
    void operator = (Semaphore&& s) = delete;
    Semaphore (Semaphore&& s) = delete;
};


ILMTHREAD_INTERNAL_NAMESPACE_HEADER_EXIT

#endif // INCLUDED_ILM_THREAD_SEMAPHORE_H