279 lines
9.1 KiB
C
279 lines
9.1 KiB
C
/*
|
|
* ptw32_MCS_lock.c
|
|
*
|
|
* Description:
|
|
* This translation unit implements queue-based locks.
|
|
*
|
|
* --------------------------------------------------------------------------
|
|
*
|
|
* Pthreads-win32 - POSIX Threads Library for Win32
|
|
* Copyright(C) 1998 John E. Bossom
|
|
* Copyright(C) 1999,2005 Pthreads-win32 contributors
|
|
*
|
|
* Contact Email: rpj@callisto.canberra.edu.au
|
|
*
|
|
* The current list of contributors is contained
|
|
* in the file CONTRIBUTORS included with the source
|
|
* code distribution. The list can also be seen at the
|
|
* following World Wide Web location:
|
|
* http://sources.redhat.com/pthreads-win32/contributors.html
|
|
*
|
|
* This library is free software; you can redistribute it and/or
|
|
* modify it under the terms of the GNU Lesser General Public
|
|
* License as published by the Free Software Foundation; either
|
|
* version 2 of the License, or (at your option) any later version.
|
|
*
|
|
* This library is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
* Lesser General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU Lesser General Public
|
|
* License along with this library in the file COPYING.LIB;
|
|
* if not, write to the Free Software Foundation, Inc.,
|
|
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
|
|
*/
|
|
|
|
/*
|
|
* About MCS locks:
|
|
*
|
|
* MCS locks are queue-based locks, where the queue nodes are local to the
|
|
* thread. The 'lock' is nothing more than a global pointer that points to
|
|
* the last node in the queue, or is NULL if the queue is empty.
|
|
*
|
|
* Originally designed for use as spin locks requiring no kernel resources
|
|
* for synchronisation or blocking, the implementation below has adapted
|
|
* the MCS spin lock for use as a general mutex that will suspend threads
|
|
* when there is lock contention.
|
|
*
|
|
* Because the queue nodes are thread-local, most of the memory read/write
|
|
* operations required to add or remove nodes from the queue do not trigger
|
|
* cache-coherence updates.
|
|
*
|
|
* Like 'named' mutexes, MCS locks consume system resources transiently -
|
|
* they are able to acquire and free resources automatically - but MCS
|
|
* locks do not require any unique 'name' to identify the lock to all
|
|
* threads using it.
|
|
*
|
|
* Usage of MCS locks:
|
|
*
|
|
* - you need a global ptw32_mcs_lock_t instance initialised to 0 or NULL.
|
|
* - you need a local thread-scope ptw32_mcs_local_node_t instance, which
|
|
* may serve several different locks but you need at least one node for
|
|
* every lock held concurrently by a thread.
|
|
*
|
|
* E.g.:
|
|
*
|
|
* ptw32_mcs_lock_t lock1 = 0;
|
|
* ptw32_mcs_lock_t lock2 = 0;
|
|
*
|
|
* void *mythread(void *arg)
|
|
* {
|
|
* ptw32_mcs_local_node_t node;
|
|
*
|
|
* ptw32_mcs_acquire (&lock1, &node);
|
|
* ptw32_mcs_lock_release (&node);
|
|
*
|
|
* ptw32_mcs_lock_acquire (&lock2, &node);
|
|
* ptw32_mcs_lock_release (&node);
|
|
* {
|
|
* ptw32_mcs_local_node_t nodex;
|
|
*
|
|
* ptw32_mcs_lock_acquire (&lock1, &node);
|
|
* ptw32_mcs_lock_acquire (&lock2, &nodex);
|
|
*
|
|
* ptw32_mcs_lock_release (&nodex);
|
|
* ptw32_mcs_lock_release (&node);
|
|
* }
|
|
* return (void *)0;
|
|
* }
|
|
*/
|
|
|
|
#include "pthread.h"
|
|
#include "sched.h"
|
|
#include "implement.h"
|
|
|
|
/*
|
|
* ptw32_mcs_flag_set -- notify another thread about an event.
|
|
*
|
|
* Set event if an event handle has been stored in the flag, and
|
|
* set flag to -1 otherwise. Note that -1 cannot be a valid handle value.
|
|
*/
|
|
INLINE void
|
|
ptw32_mcs_flag_set (HANDLE * flag)
|
|
{
|
|
HANDLE e = (HANDLE)(PTW32_INTERLOCKED_SIZE)PTW32_INTERLOCKED_COMPARE_EXCHANGE_SIZE(
|
|
(PTW32_INTERLOCKED_SIZEPTR)flag,
|
|
(PTW32_INTERLOCKED_SIZE)-1,
|
|
(PTW32_INTERLOCKED_SIZE)0);
|
|
if ((HANDLE)0 != e)
|
|
{
|
|
/* another thread has already stored an event handle in the flag */
|
|
SetEvent(e);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* ptw32_mcs_flag_set -- wait for notification from another.
|
|
*
|
|
* Store an event handle in the flag and wait on it if the flag has not been
|
|
* set, and proceed without creating an event otherwise.
|
|
*/
|
|
INLINE void
|
|
ptw32_mcs_flag_wait (HANDLE * flag)
|
|
{
|
|
if ((PTW32_INTERLOCKED_LONG)0 ==
|
|
PTW32_INTERLOCKED_EXCHANGE_ADD_SIZE((PTW32_INTERLOCKED_SIZEPTR)flag,
|
|
(PTW32_INTERLOCKED_SIZE)0)) /* MBR fence */
|
|
{
|
|
/* the flag is not set. create event. */
|
|
|
|
HANDLE e = CreateEvent(NULL, PTW32_FALSE, PTW32_FALSE, NULL);
|
|
|
|
if ((PTW32_INTERLOCKED_SIZE)0 == PTW32_INTERLOCKED_COMPARE_EXCHANGE_SIZE(
|
|
(PTW32_INTERLOCKED_SIZEPTR)flag,
|
|
(PTW32_INTERLOCKED_SIZE)e,
|
|
(PTW32_INTERLOCKED_SIZE)0))
|
|
{
|
|
/* stored handle in the flag. wait on it now. */
|
|
WaitForSingleObject(e, INFINITE);
|
|
}
|
|
|
|
CloseHandle(e);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* ptw32_mcs_lock_acquire -- acquire an MCS lock.
|
|
*
|
|
* See:
|
|
* J. M. Mellor-Crummey and M. L. Scott.
|
|
* Algorithms for Scalable Synchronization on Shared-Memory Multiprocessors.
|
|
* ACM Transactions on Computer Systems, 9(1):21-65, Feb. 1991.
|
|
*/
|
|
#if defined(PTW32_BUILD_INLINED)
|
|
INLINE
|
|
#endif /* PTW32_BUILD_INLINED */
|
|
void
|
|
ptw32_mcs_lock_acquire (ptw32_mcs_lock_t * lock, ptw32_mcs_local_node_t * node)
|
|
{
|
|
ptw32_mcs_local_node_t *pred;
|
|
|
|
node->lock = lock;
|
|
node->nextFlag = 0;
|
|
node->readyFlag = 0;
|
|
node->next = 0; /* initially, no successor */
|
|
|
|
/* queue for the lock */
|
|
pred = (ptw32_mcs_local_node_t *)PTW32_INTERLOCKED_EXCHANGE_PTR((PTW32_INTERLOCKED_PVOID_PTR)lock,
|
|
(PTW32_INTERLOCKED_PVOID)node);
|
|
|
|
if (0 != pred)
|
|
{
|
|
/* the lock was not free. link behind predecessor. */
|
|
pred->next = node;
|
|
ptw32_mcs_flag_set(&pred->nextFlag);
|
|
ptw32_mcs_flag_wait(&node->readyFlag);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* ptw32_mcs_lock_release -- release an MCS lock.
|
|
*
|
|
* See:
|
|
* J. M. Mellor-Crummey and M. L. Scott.
|
|
* Algorithms for Scalable Synchronization on Shared-Memory Multiprocessors.
|
|
* ACM Transactions on Computer Systems, 9(1):21-65, Feb. 1991.
|
|
*/
|
|
#if defined(PTW32_BUILD_INLINED)
|
|
INLINE
|
|
#endif /* PTW32_BUILD_INLINED */
|
|
void
|
|
ptw32_mcs_lock_release (ptw32_mcs_local_node_t * node)
|
|
{
|
|
ptw32_mcs_lock_t *lock = node->lock;
|
|
ptw32_mcs_local_node_t *next =
|
|
(ptw32_mcs_local_node_t *)
|
|
PTW32_INTERLOCKED_EXCHANGE_ADD_SIZE((PTW32_INTERLOCKED_SIZEPTR)&node->next, (PTW32_INTERLOCKED_SIZE)0); /* MBR fence */
|
|
|
|
if (0 == next)
|
|
{
|
|
/* no known successor */
|
|
|
|
if (node == (ptw32_mcs_local_node_t *)
|
|
PTW32_INTERLOCKED_COMPARE_EXCHANGE_PTR((PTW32_INTERLOCKED_PVOID_PTR)lock,
|
|
(PTW32_INTERLOCKED_PVOID)0,
|
|
(PTW32_INTERLOCKED_PVOID)node))
|
|
{
|
|
/* no successor, lock is free now */
|
|
return;
|
|
}
|
|
|
|
/* A successor has started enqueueing behind us so wait for them to link to us */
|
|
ptw32_mcs_flag_wait(&node->nextFlag);
|
|
next = (ptw32_mcs_local_node_t *)
|
|
PTW32_INTERLOCKED_EXCHANGE_ADD_SIZE((PTW32_INTERLOCKED_SIZEPTR)&node->next, (PTW32_INTERLOCKED_SIZE)0); /* MBR fence */
|
|
}
|
|
|
|
/* pass the lock */
|
|
ptw32_mcs_flag_set(&next->readyFlag);
|
|
}
|
|
|
|
/*
|
|
* ptw32_mcs_lock_try_acquire
|
|
*/
|
|
#if defined(PTW32_BUILD_INLINED)
|
|
INLINE
|
|
#endif /* PTW32_BUILD_INLINED */
|
|
int
|
|
ptw32_mcs_lock_try_acquire (ptw32_mcs_lock_t * lock, ptw32_mcs_local_node_t * node)
|
|
{
|
|
node->lock = lock;
|
|
node->nextFlag = 0;
|
|
node->readyFlag = 0;
|
|
node->next = 0; /* initially, no successor */
|
|
|
|
return ((PTW32_INTERLOCKED_PVOID)PTW32_INTERLOCKED_COMPARE_EXCHANGE_PTR((PTW32_INTERLOCKED_PVOID_PTR)lock,
|
|
(PTW32_INTERLOCKED_PVOID)node,
|
|
(PTW32_INTERLOCKED_PVOID)0)
|
|
== (PTW32_INTERLOCKED_PVOID)0) ? 0 : EBUSY;
|
|
}
|
|
|
|
/*
|
|
* ptw32_mcs_node_transfer -- move an MCS lock local node, usually from thread
|
|
* space to, for example, global space so that another thread can release
|
|
* the lock on behalf of the current lock owner.
|
|
*
|
|
* Example: used in pthread_barrier_wait where we want the last thread out of
|
|
* the barrier to release the lock owned by the last thread to enter the barrier
|
|
* (the one that releases all threads but not necessarily the last to leave).
|
|
*
|
|
* Should only be called by the thread that has the lock.
|
|
*/
|
|
#if defined(PTW32_BUILD_INLINED)
|
|
INLINE
|
|
#endif /* PTW32_BUILD_INLINED */
|
|
void
|
|
ptw32_mcs_node_transfer (ptw32_mcs_local_node_t * new_node, ptw32_mcs_local_node_t * old_node)
|
|
{
|
|
new_node->lock = old_node->lock;
|
|
new_node->nextFlag = 0; /* Not needed - used only in initial Acquire */
|
|
new_node->readyFlag = 0; /* Not needed - we were waiting on this */
|
|
new_node->next = 0;
|
|
|
|
if ((ptw32_mcs_local_node_t *)PTW32_INTERLOCKED_COMPARE_EXCHANGE_PTR((PTW32_INTERLOCKED_PVOID_PTR)new_node->lock,
|
|
(PTW32_INTERLOCKED_PVOID)new_node,
|
|
(PTW32_INTERLOCKED_PVOID)old_node)
|
|
!= old_node)
|
|
{
|
|
/*
|
|
* A successor has queued after us, so wait for them to link to us
|
|
*/
|
|
while (old_node->next == 0)
|
|
{
|
|
sched_yield();
|
|
}
|
|
new_node->next = old_node->next;
|
|
}
|
|
}
|