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Diffstat (limited to 'ptw32_MCS_lock.c')
| -rw-r--r-- | ptw32_MCS_lock.c | 210 |
1 files changed, 210 insertions, 0 deletions
diff --git a/ptw32_MCS_lock.c b/ptw32_MCS_lock.c new file mode 100644 index 0000000..478a059 --- /dev/null +++ b/ptw32_MCS_lock.c @@ -0,0 +1,210 @@ +/* + * 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., + * 59 Temple Place - Suite 330, Boston, MA 02111-1307, 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 recourses transiently - + * they are able to acquire and free recourses 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_release (&node); + * + * ptw32_mcs_acquire (&lock2, &node); + * ptw32_mcs_release (&node); + * { + * ptw32_mcs_local_node_t nodex; + * + * ptw32_mcs_acquire (&lock1, &node); + * ptw32_mcs_acquire (&lock2, &nodex); + * + * ptw32_mcs_release (&nodex); + * ptw32_mcs_release (&node); + * } + * return (void *)0; + * } + */ + +#include "implement.h" +#include "pthread.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 (LONG * flag) +{ + HANDLE e = (HANDLE)PTW32_INTERLOCKED_COMPARE_EXCHANGE( + (PTW32_INTERLOCKED_LPLONG)flag, + (PTW32_INTERLOCKED_LONG)-1, + (PTW32_INTERLOCKED_LONG)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 (LONG * flag) +{ + if (0 == InterlockedExchangeAdd((LPLONG)flag, 0)) /* MBR fence */ + { + /* the flag is not set. create event. */ + + HANDLE e = CreateEvent(NULL, PTW32_FALSE, PTW32_FALSE, NULL); + + if (0 == PTW32_INTERLOCKED_COMPARE_EXCHANGE( + (PTW32_INTERLOCKED_LPLONG)flag, + (PTW32_INTERLOCKED_LONG)e, + (PTW32_INTERLOCKED_LONG)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. + */ +INLINE 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((LPLONG)lock, + (LONG)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. + */ +INLINE 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 *) + InterlockedExchangeAdd((LPLONG)&node->next, 0); /* MBR fence */ + + if (0 == next) + { + /* no known successor */ + + if (node == (ptw32_mcs_local_node_t *) + PTW32_INTERLOCKED_COMPARE_EXCHANGE((PTW32_INTERLOCKED_LPLONG)lock, + (PTW32_INTERLOCKED_LONG)0, + (PTW32_INTERLOCKED_LONG)node)) + { + /* no successor, lock is free now */ + return; + } + + /* wait for successor */ + ptw32_mcs_flag_wait(&node->nextFlag); + next = (ptw32_mcs_local_node_t *) + InterlockedExchangeAdd((LPLONG)&node->next, 0); /* MBR fence */ + } + + /* pass the lock */ + ptw32_mcs_flag_set(&next->readyFlag); +} |