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//---------------------------------------------------------
// For conditions of distribution and use, see
// https://github.com/preshing/cpp11-on-multicore/blob/master/LICENSE
//---------------------------------------------------------
#ifndef __CPP11OM_BENAPHORE_H__
#define __CPP11OM_BENAPHORE_H__
#include <cassert>
#include <thread>
#include <atomic>
#include "sema.h"
//---------------------------------------------------------
// NonRecursiveBenaphore
//---------------------------------------------------------
class NonRecursiveBenaphore
{
private:
std::atomic<int> m_contentionCount;
DefaultSemaphoreType m_sema;
public:
NonRecursiveBenaphore() : m_contentionCount(0) {}
void lock()
{
if (m_contentionCount.fetch_add(1, std::memory_order_acquire) > 0)
{
m_sema.wait();
}
}
bool tryLock()
{
if (m_contentionCount.load(std::memory_order_relaxed) != 0)
return false;
int expected = 0;
return m_contentionCount.compare_exchange_strong(expected, 1, std::memory_order_acquire);
}
void unlock()
{
int oldCount = m_contentionCount.fetch_sub(1, std::memory_order_release);
assert(oldCount > 0);
if (oldCount > 1)
{
m_sema.signal();
}
}
};
//---------------------------------------------------------
// RecursiveBenaphore
//---------------------------------------------------------
class RecursiveBenaphore
{
private:
std::atomic<int> m_contentionCount;
std::atomic<std::thread::id> m_owner;
int m_recursion;
DefaultSemaphoreType m_sema;
public:
RecursiveBenaphore()
: m_contentionCount(0)
// Apple LLVM 6.0 (in Xcode 6.1) refuses to initialize m_owner from a std::thread::id.
// "error: no viable conversion from 'std::__1::__thread_id' to '_Atomic(std::__1::__thread_id)'"
// (Note: On Linux, as of April 11, 2015, Clang 3.7 & libc++ don't have this problem.)
// Prefer atomic_init (below) when Apple LLVM is detected.
#if !(defined(__llvm__) && defined(__APPLE__))
, m_owner(std::thread::id())
#endif
, m_recursion(0)
{
// GCC 4.7.2's libstdc++-v3 doesn't implement atomic_init.
// "warning: inline function 'void std::atomic_init(std::atomic<_ITp>*, _ITp) [with _ITp = std::thread::id]' used but never defined [enabled by default]"
// Using the constructor (above) in that case.
#if (defined(__llvm__) && defined(__APPLE__))
std::atomic_init(&m_owner, std::thread::id());
#endif
// If this assert fails on your system, you'll have to replace std::thread::id with a
// more compact, platform-specific thread ID, or just comment the assert and live with
// the extra overhead.
assert(m_owner.is_lock_free());
}
void lock()
{
std::thread::id tid = std::this_thread::get_id();
if (m_contentionCount.fetch_add(1, std::memory_order_acquire) > 0)
{
if (tid != m_owner.load(std::memory_order_relaxed))
m_sema.wait();
}
//--- We are now inside the lock ---
m_owner.store(tid, std::memory_order_relaxed);
m_recursion++;
}
bool tryLock()
{
std::thread::id tid = std::this_thread::get_id();
if (m_owner.load(std::memory_order_relaxed) == tid)
{
// Already inside the lock
m_contentionCount.fetch_add(1, std::memory_order_relaxed);
}
else
{
if (m_contentionCount.load(std::memory_order_relaxed) != 0)
return false;
int expected = 0;
if (!m_contentionCount.compare_exchange_strong(expected, 1, std::memory_order_acquire))
return false;
//--- We are now inside the lock ---
m_owner.store(tid, std::memory_order_relaxed);
}
m_recursion++;
return true;
}
void unlock()
{
assert(std::this_thread::get_id() == m_owner.load(std::memory_order_relaxed));
int recur = --m_recursion;
if (recur == 0)
m_owner.store(std::thread::id(), std::memory_order_relaxed);
if (m_contentionCount.fetch_sub(1, std::memory_order_release) > 1)
{
if (recur == 0)
m_sema.signal();
}
//--- We are now outside the lock ---
}
};
#endif // __CPP11OM_BENAPHORE_H__