Subject: [Boost-commit] svn:boost r85785 - trunk/boost/sync/detail/event
From: tim_at_[hidden]
Date: 2013-09-19 04:15:59
Author: timblechmann
Date: 2013-09-19 04:15:59 EDT (Thu, 19 Sep 2013)
New Revision: 85785
URL: http://svn.boost.org/trac/boost/changeset/85785
Log:
sync: event - avoid possible ABA problem in mach implementation
Text files modified:
trunk/boost/sync/detail/event/event_mach.hpp | 58 ++++++++++++++++++++-------------------
1 files changed, 30 insertions(+), 28 deletions(-)
Modified: trunk/boost/sync/detail/event/event_mach.hpp
==============================================================================
--- trunk/boost/sync/detail/event/event_mach.hpp Thu Sep 19 04:15:37 2013 (r85784)
+++ trunk/boost/sync/detail/event/event_mach.hpp 2013-09-19 04:15:59 EDT (Thu, 19 Sep 2013) (r85785)
@@ -1,6 +1,7 @@
// event.hpp, mach events
//
// Copyright (C) 2013 Tim Blechmann
+// Copyright (C) 2013 Andrey Semashev
//
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
@@ -11,6 +12,7 @@
#include <cstddef>
#include <boost/assert.hpp>
+#include <boost/cstdint.hpp>
#include <boost/sync/detail/config.hpp>
#include <boost/sync/exceptions/resource_error.hpp>
@@ -37,7 +39,7 @@
public:
explicit event(bool auto_reset = false):
- m_auto_reset(auto_reset), m_signaled(0)
+ m_auto_reset(auto_reset), m_state(0)
{
kern_return_t result = semaphore_create(mach_task_self(), &m_sem, SYNC_POLICY_FIFO, 0);
BOOST_VERIFY(result == KERN_SUCCESS);
@@ -52,38 +54,42 @@
void post()
{
if (m_auto_reset) {
- bool already_signaled = m_signaled.exchange(true);
- if (!already_signaled)
- semaphore_signal( m_sem ); // wake one thread!
+ bool was_signalled;
+
+ 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 (!was_signalled)
+ semaphore_signal(m_sem); // wake one thread!
} else {
- m_signaled = true;
+ m_state.store( 1, memory_order_release );
semaphore_signal_all( m_sem ); // wake all threads!& reset semaphore count
}
}
void reset()
{
- m_signaled = false;
+ m_state = 0; // CHECK: do we need to increment the ABA tag?
}
void wait()
{
if (m_auto_reset) {
- // the first waiter succeeds and resets the signalled state
-
- try_again:
kern_return_t result = semaphore_wait( m_sem );
BOOST_VERIFY (result == KERN_SUCCESS);
- bool isTrue = true;
- bool firstWaiter = m_signaled.compare_exchange_strong(isTrue, false);
-
- if (firstWaiter) // only the first waiter succeeds
- return;
+ 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
- goto try_again;
} else {
- if (m_signaled.load() == true)
+ if (m_state.load(memory_order_acquire) == 1)
return;
kern_return_t result = semaphore_wait( m_sem );
@@ -117,21 +123,17 @@
bool do_try_wait_until (const mach_timespec_t & timeout)
{
if (m_auto_reset) {
- // the first waiter succeeds and resets the signaled state
-
kern_return_t result = semaphore_timedwait( m_sem, timeout );
if (result == KERN_SUCCESS) {
- bool isTrue = true;
- bool firstWaiter = m_signaled.compare_exchange_strong(isTrue, false);
-
- if (firstWaiter) // only the first waiter succeeds
- return true;
- }
- return false;
-
+ 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
+ return true;
+ } else
+ return false;
} else {
- if (m_signaled.load() == true)
+ if (m_state.load( memory_order_acquire ) == 1)
return true;
kern_return_t result = semaphore_timedwait( m_sem, timeout );
@@ -144,7 +146,7 @@
const bool m_auto_reset;
semaphore_t m_sem;
- atomic_bool m_signaled;
+ atomic<uint32_t> m_state;
};
}