bslmt_semaphoreimpl_counted.h

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/// @file bslmt_semaphoreimpl_counted.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslmt_semaphoreimpl_counted.h                                      -*-C++-*-
#ifndef INCLUDED_BSLMT_SEMAPHOREIMPL_COUNTED
#define INCLUDED_BSLMT_SEMAPHOREIMPL_COUNTED
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslmt_semaphoreimpl_counted bslmt_semaphoreimpl_counted
/// @brief  Provide an implementation of `bslmt::Semaphore` with count.
/// @addtogroup bsl
/// @{
/// @addtogroup bslmt
/// @{
/// @addtogroup bslmt_semaphoreimpl_counted
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslmt_semaphoreimpl_counted-purpose"> Purpose</a>
/// * <a href="#bslmt_semaphoreimpl_counted-classes"> Classes </a>
/// * <a href="#bslmt_semaphoreimpl_counted-description"> Description </a>
///   * <a href="#bslmt_semaphoreimpl_counted-usage"> Usage </a>
///
/// # Purpose {#bslmt_semaphoreimpl_counted-purpose}
/// Provide an implementation of `bslmt::Semaphore` with count.
///
/// # Classes {#bslmt_semaphoreimpl_counted-classes}
///
/// -  bslmt::SemaphoreImpl<CountedSemaphore>: semaphore specialization with count
///
/// @see  bslmt_semaphore
///
/// # Description {#bslmt_semaphoreimpl_counted-description}
/// This component provides an implementation of
/// `bslmt::Semaphore`, `bslmt::SemaphoreImpl<CountedSemaphore>`, via the
/// template specialization:
/// @code
/// bslmt::SemaphoreImpl<Platform::CountedSemaphore>
/// @endcode
/// This template class should not be used (directly) by client code.  Clients
/// should instead use `bslmt::Semaphore`.
///
/// This implementation of `bslmt::Semaphore` is intended for platforms where a
/// separate count must be maintained.  `bslmt::Semaphore` supports large
/// values, but the native semaphores provided on some platforms are restricted
/// to a relatively small range of values (e.g., `[ 0 .. 32000 ]` on AIX) and on
/// some other platforms do not provide a count at all (Darwin).  To support
/// uniform usage across platforms, this component maintains the count of the
/// semaphore in a separate atomic integer.  `post` is only invoked on the
/// underlying semaphore when it is known there are threads blocked on it.
///
/// ## Usage {#bslmt_semaphoreimpl_counted-usage}
///
///
/// This component is an implementation detail of `bslmt` and is *not* intended
/// for direct client use.  It is subject to change without notice.  As such, a
/// usage example is not provided.
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslmt
 * @{
 */
/** @addtogroup bslmt_semaphoreimpl_counted
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslmt_platform.h>
 
#ifdef BSLMT_PLATFORM_COUNTED_SEMAPHORE
 
// Platform-specific implementation starts here.
 
#include <bsls_atomic.h>
 
#include <bslmt_semaphoreimpl_pthread.h>
#include <bslmt_semaphoreimpl_darwin.h>
 
 
namespace bslmt {
 
template <class SEMAPHORE_POLICY>
class SemaphoreImpl;
 
             // ===============================================
             // class SemaphoreImpl<Platform::CountedSemaphore>
             // ===============================================
 
/// This class provides a full specialization of `SemaphoreImpl` with a
/// separate count variable.  This implementation maintains the value of the
/// semaphore in a separate atomic integer count, so as to allow for
/// semaphore count on platforms where a semaphore implementation doesn't
/// provide the count or the provided count has very limited range of
/// values.
template <>
class SemaphoreImpl<Platform::CountedSemaphore> {
 
    // DATA
    bsls::AtomicInt d_resources; // if positive, number of available resources
                                 // if negative: number of waiting threads
 
    SemaphoreImpl<Platform::CountedSemaphoreImplPolicy>
                    d_sem;       // platform semaphore implementation
 
  private:
    // NOT IMPLEMENTED
    SemaphoreImpl(const SemaphoreImpl&);
    SemaphoreImpl& operator=(const SemaphoreImpl&);
 
  public:
    // CREATORS
 
    /// Create a semaphore.  This method does not return normally unless
    /// there are sufficient system resources to construct the object.
    SemaphoreImpl(int count);
 
    /// Destroy a semaphore
    ~SemaphoreImpl();
 
    // MANIPULATORS
 
    /// Atomically increment the count of this semaphore.
    void post();
 
    /// Atomically increment the count of this semaphore by the specified `number`.  
    /// 
    /// \pre The behavior is undefined   unless `number > 0`.
    void post(int number);
 
    /// Decrement the count of this semaphore if it is positive and return
    /// 0.  Return a non-zero value otherwise.
    int tryWait();
 
    /// Block until the count of this semaphore is a positive value and
    /// atomically decrement it.
    void wait();
 
    // ACCESSORS
 
    /// Return the current value of this semaphore.
    int getValue() const;
};
 
// ============================================================================
//                             INLINE DEFINITIONS
// ============================================================================
 
             // -----------------------------------------------
             // class SemaphoreImpl<Platform::CountedSemaphore>
             // -----------------------------------------------
 
// CREATORS
inline
SemaphoreImpl<bslmt::Platform::CountedSemaphore>::SemaphoreImpl(
                                                                     int count)
: d_resources(count)
, d_sem(0)
{
}
 
inline
SemaphoreImpl<bslmt::Platform::CountedSemaphore>::~SemaphoreImpl()
{
}
 
// MANIPULATORS
inline
void SemaphoreImpl<bslmt::Platform::CountedSemaphore>::post()
{
    if (++d_resources <= 0) {
        d_sem.post();
    }
}
 
inline
void SemaphoreImpl<bslmt::Platform::CountedSemaphore>::post(int number)
{
    for (int i = 0; i < number; ++i) {
        post();
    }
}
 
inline
int SemaphoreImpl<bslmt::Platform::CountedSemaphore>::tryWait()
{
    for (int i = d_resources; i > 0; i = d_resources) {
        if (i == d_resources.testAndSwap(i, i - 1)) {
            return 0;
        }
    }
 
    return -1;
}
 
inline
void SemaphoreImpl<bslmt::Platform::CountedSemaphore>::wait()
{
    if (--d_resources >= 0) {
        return;
    }
 
    d_sem.wait();
}
 
// ACCESSORS
inline
int SemaphoreImpl<bslmt::Platform::CountedSemaphore>::getValue() const
{
    const int v = d_resources;
    return v > 0 ? v : 0;
}
 
}  // close package namespace
 
 
#endif
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2015 Bloomberg Finance L.P.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ----------------------------- END-OF-FILE ----------------------------------
 
/** @} */
/** @} */
/** @} */