Subject: [Boost-commit] svn:boost r85845 - trunk/boost/sync/detail/event
From: tim_at_[hidden]
Date: 2013-09-23 03:41:33
Author: timblechmann
Date: 2013-09-23 03:41:33 EDT (Mon, 23 Sep 2013)
New Revision: 85845
URL: http://svn.boost.org/trac/boost/changeset/85845
Log:
sync: event - fix mach-semaphore emulation
Text files modified:
trunk/boost/sync/detail/event/event_mach.hpp | 53 ++++++++++++++++++++-------------------
1 files changed, 27 insertions(+), 26 deletions(-)
Modified: trunk/boost/sync/detail/event/event_mach.hpp
==============================================================================
--- trunk/boost/sync/detail/event/event_mach.hpp Mon Sep 23 03:41:08 2013 (r85844)
+++ trunk/boost/sync/detail/event/event_mach.hpp 2013-09-23 03:41:33 EDT (Mon, 23 Sep 2013) (r85845)
@@ -1,3 +1,4 @@
+
// event.hpp, mach events
//
// Copyright (C) 2013 Tim Blechmann
@@ -12,9 +13,11 @@
#include <cstddef>
#include <boost/assert.hpp>
+#include <boost/atomic.hpp>
#include <boost/cstdint.hpp>
#include <boost/sync/detail/config.hpp>
+#include <boost/sync/detail/pause.hpp>
#include <boost/sync/exceptions/resource_error.hpp>
#include <mach/task.h>
@@ -22,8 +25,6 @@
#include <mach/mach_traps.h>
#include <mach/mach_init.h>
-#include <boost/atomic.hpp>
-
#include <boost/sync/detail/header.hpp>
namespace boost {
@@ -54,19 +55,22 @@
void post() BOOST_NOEXCEPT
{
if (m_auto_reset) {
- bool was_signalled;
+ int32_t old_state = m_state.load(memory_order_acquire);
+ if (old_state >= 0) {
+ for (;;) {
+ if (m_state.compare_exchange_weak( old_state, old_state - 1, memory_order_release, memory_order_acquire)) {
+ semaphore_signal( m_sem );
+ return; // avoid unnecessary fence
+ }
- uint32_t old_state = m_state.load( memory_order_acquire );
- for(;;) {
- was_signalled = ((old_state & 1u) != 0);
- uint32_t new_state = ((old_state + 2u) | 1u) & std::numeric_limits<uint32_t>::max();
- if ( m_state.compare_exchange_weak( old_state, new_state, memory_order_release, memory_order_acquire ) )
- break;
- // backoff
+ if (old_state < 0)
+ break; // someone else has set the event with no waiters
+
+ detail::pause();
+ }
}
- if (!was_signalled)
- semaphore_signal(m_sem); // wake one thread!
+ atomic_thread_fence( memory_order_release );
} else {
m_state.store( 1, memory_order_release );
semaphore_signal_all( m_sem ); // wake all threads!& reset semaphore count
@@ -75,19 +79,16 @@
void reset() BOOST_NOEXCEPT
{
- m_state = 0; // CHECK: do we need to increment the ABA tag?
+ m_state = 0;
}
void wait() BOOST_NOEXCEPT
{
if (m_auto_reset) {
+ m_state.fetch_add(1, memory_order_acquire);
+
kern_return_t result = semaphore_wait( m_sem );
BOOST_VERIFY (result == KERN_SUCCESS);
-
- uint32_t old_state = m_state.load(memory_order_acquire);
- if (!m_state.compare_exchange_strong( old_state, old_state & ~1u, memory_order_release, memory_order_acquire ) )
- semaphore_signal(m_sem); // another post succeeded, wake up another thread
-
} else {
if (m_state.load(memory_order_acquire) == 1)
return;
@@ -123,15 +124,15 @@
bool do_try_wait_until (const mach_timespec_t & timeout)
{
if (m_auto_reset) {
- kern_return_t result = semaphore_timedwait( m_sem, timeout );
+ m_state.fetch_add(1, memory_order_acquire);
- if (result == KERN_SUCCESS) {
- uint32_t old_state = m_state.load(memory_order_acquire);
- if (!m_state.compare_exchange_strong( old_state, old_state & ~1u, memory_order_release, memory_order_acquire ) )
- semaphore_signal(m_sem); // another post succeeded, wake up another thread
+ kern_return_t result = semaphore_timedwait( m_sem, timeout );
+ if (result == KERN_SUCCESS)
return true;
- } else
- return false;
+
+ m_state.fetch_add(-1, memory_order_relaxed);
+ return false;
+
} else {
if (m_state.load( memory_order_acquire ) == 1)
return true;
@@ -146,7 +147,7 @@
const bool m_auto_reset;
semaphore_t m_sem;
- atomic<uint32_t> m_state;
+ atomic<int32_t> m_state;
};
}