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Diffstat (limited to 'libpthread/linuxthreads.old/rwlock.c')
| -rw-r--r-- | libpthread/linuxthreads.old/rwlock.c | 485 |
1 files changed, 485 insertions, 0 deletions
diff --git a/libpthread/linuxthreads.old/rwlock.c b/libpthread/linuxthreads.old/rwlock.c new file mode 100644 index 000000000..3ab940261 --- /dev/null +++ b/libpthread/linuxthreads.old/rwlock.c @@ -0,0 +1,485 @@ +/* Read-write lock implementation. + Copyright (C) 1998 Free Software Foundation, Inc. + This file is part of the GNU C Library. + Contributed by Xavier Leroy <Xavier.Leroy@inria.fr> + and Ulrich Drepper <drepper@cygnus.com>, 1998. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Library General Public License as + published by the Free Software Foundation; either version 2 of the + License, or (at your option) any later version. + + The GNU C 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 + Library General Public License for more details. + + You should have received a copy of the GNU Library General Public + License along with the GNU C Library; see the file COPYING.LIB. If not, + see <http://www.gnu.org/licenses/>. */ + +#include <errno.h> +#include <pthread.h> +#include <stdlib.h> +#include "internals.h" +#include "queue.h" +#include "spinlock.h" +#include "restart.h" + +/* + * Check whether the calling thread already owns one or more read locks on the + * specified lock. If so, return a pointer to the read lock info structure + * corresponding to that lock. + */ + +static pthread_readlock_info * +rwlock_is_in_list(pthread_descr self, pthread_rwlock_t *rwlock) +{ + pthread_readlock_info *info; + + for (info = self->p_readlock_list; info != NULL; info = info->pr_next) + { + if (info->pr_lock == rwlock) + return info; + } + + return NULL; +} + +/* + * Add a new lock to the thread's list of locks for which it has a read lock. + * A new info node must be allocated for this, which is taken from the thread's + * free list, or by calling malloc. If malloc fails, a null pointer is + * returned. Otherwise the lock info structure is initialized and pushed + * onto the thread's list. + */ + +static pthread_readlock_info * +rwlock_add_to_list(pthread_descr self, pthread_rwlock_t *rwlock) +{ + pthread_readlock_info *info = self->p_readlock_free; + + if (info != NULL) + self->p_readlock_free = info->pr_next; + else + info = malloc(sizeof *info); + + if (info == NULL) + return NULL; + + info->pr_lock_count = 1; + info->pr_lock = rwlock; + info->pr_next = self->p_readlock_list; + self->p_readlock_list = info; + + return info; +} + +/* + * If the thread owns a read lock over the given pthread_rwlock_t, + * and this read lock is tracked in the thread's lock list, + * this function returns a pointer to the info node in that list. + * It also decrements the lock count within that node, and if + * it reaches zero, it removes the node from the list. + * If nothing is found, it returns a null pointer. + */ + +static pthread_readlock_info * +rwlock_remove_from_list(pthread_descr self, pthread_rwlock_t *rwlock) +{ + pthread_readlock_info **pinfo; + + for (pinfo = &self->p_readlock_list; *pinfo != NULL; pinfo = &(*pinfo)->pr_next) + { + if ((*pinfo)->pr_lock == rwlock) + { + pthread_readlock_info *info = *pinfo; + if (--info->pr_lock_count == 0) + *pinfo = info->pr_next; + return info; + } + } + + return NULL; +} + +/* + * This function checks whether the conditions are right to place a read lock. + * It returns 1 if so, otherwise zero. The rwlock's internal lock must be + * locked upon entry. + */ + +static int +rwlock_can_rdlock(pthread_rwlock_t *rwlock, int have_lock_already) +{ + /* Can't readlock; it is write locked. */ + if (rwlock->__rw_writer != NULL) + return 0; + + /* Lock prefers readers; get it. */ + if (rwlock->__rw_kind == PTHREAD_RWLOCK_PREFER_READER_NP) + return 1; + + /* Lock prefers writers, but none are waiting. */ + if (queue_is_empty(&rwlock->__rw_write_waiting)) + return 1; + + /* Writers are waiting, but this thread already has a read lock */ + if (have_lock_already) + return 1; + + /* Writers are waiting, and this is a new lock */ + return 0; +} + +/* + * This function helps support brain-damaged recursive read locking + * semantics required by Unix 98, while maintaining write priority. + * This basically determines whether this thread already holds a read lock + * already. It returns 1 if so, otherwise it returns 0. + * + * If the thread has any ``untracked read locks'' then it just assumes + * that this lock is among them, just to be safe, and returns 1. + * + * Also, if it finds the thread's lock in the list, it sets the pointer + * referenced by pexisting to refer to the list entry. + * + * If the thread has no untracked locks, and the lock is not found + * in its list, then it is added to the list. If this fails, + * then *pout_of_mem is set to 1. + */ + +static int +rwlock_have_already(pthread_descr *pself, pthread_rwlock_t *rwlock, + pthread_readlock_info **pexisting, int *pout_of_mem) +{ + pthread_readlock_info *existing = NULL; + int out_of_mem = 0, have_lock_already = 0; + pthread_descr self = *pself; + + if (rwlock->__rw_kind == PTHREAD_RWLOCK_PREFER_WRITER_NP) + { + if (!self) + self = thread_self(); + + existing = rwlock_is_in_list(self, rwlock); + + if (existing != NULL || self->p_untracked_readlock_count > 0) + have_lock_already = 1; + else + { + existing = rwlock_add_to_list(self, rwlock); + if (existing == NULL) + out_of_mem = 1; + } + } + + *pout_of_mem = out_of_mem; + *pexisting = existing; + *pself = self; + + return have_lock_already; +} + +int +pthread_rwlock_init (pthread_rwlock_t *rwlock, + const pthread_rwlockattr_t *attr) +{ + __pthread_init_lock(&rwlock->__rw_lock); + rwlock->__rw_readers = 0; + rwlock->__rw_writer = NULL; + rwlock->__rw_read_waiting = NULL; + rwlock->__rw_write_waiting = NULL; + + if (attr == NULL) + { + rwlock->__rw_kind = PTHREAD_RWLOCK_DEFAULT_NP; + rwlock->__rw_pshared = PTHREAD_PROCESS_PRIVATE; + } + else + { + rwlock->__rw_kind = attr->__lockkind; + rwlock->__rw_pshared = attr->__pshared; + } + + return 0; +} + + +int +pthread_rwlock_destroy (pthread_rwlock_t *rwlock) +{ + int readers; + _pthread_descr writer; + + __pthread_lock (&rwlock->__rw_lock, NULL); + readers = rwlock->__rw_readers; + writer = rwlock->__rw_writer; + __pthread_unlock (&rwlock->__rw_lock); + + if (readers > 0 || writer != NULL) + return EBUSY; + + return 0; +} + +int +pthread_rwlock_rdlock (pthread_rwlock_t *rwlock) +{ + pthread_descr self = NULL; + pthread_readlock_info *existing; + int out_of_mem, have_lock_already; + + have_lock_already = rwlock_have_already(&self, rwlock, + &existing, &out_of_mem); + + for (;;) + { + if (self == NULL) + self = thread_self (); + + __pthread_lock (&rwlock->__rw_lock, self); + + if (rwlock_can_rdlock(rwlock, have_lock_already)) + break; + + enqueue (&rwlock->__rw_read_waiting, self); + __pthread_unlock (&rwlock->__rw_lock); + suspend (self); /* This is not a cancellation point */ + } + + ++rwlock->__rw_readers; + __pthread_unlock (&rwlock->__rw_lock); + + if (have_lock_already || out_of_mem) + { + if (existing != NULL) + existing->pr_lock_count++; + else + self->p_untracked_readlock_count++; + } + + return 0; +} + +int +pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock) +{ + pthread_descr self = thread_self(); + pthread_readlock_info *existing; + int out_of_mem, have_lock_already; + int retval = EBUSY; + + have_lock_already = rwlock_have_already(&self, rwlock, + &existing, &out_of_mem); + + __pthread_lock (&rwlock->__rw_lock, self); + + /* 0 is passed to here instead of have_lock_already. + This is to meet Single Unix Spec requirements: + if writers are waiting, pthread_rwlock_tryrdlock + does not acquire a read lock, even if the caller has + one or more read locks already. */ + + if (rwlock_can_rdlock(rwlock, 0)) + { + ++rwlock->__rw_readers; + retval = 0; + } + + __pthread_unlock (&rwlock->__rw_lock); + + if (retval == 0) + { + if (have_lock_already || out_of_mem) + { + if (existing != NULL) + existing->pr_lock_count++; + else + self->p_untracked_readlock_count++; + } + } + + return retval; +} + + +int +pthread_rwlock_wrlock (pthread_rwlock_t *rwlock) +{ + pthread_descr self = thread_self (); + + while(1) + { + __pthread_lock (&rwlock->__rw_lock, self); + if (rwlock->__rw_readers == 0 && rwlock->__rw_writer == NULL) + { + rwlock->__rw_writer = self; + __pthread_unlock (&rwlock->__rw_lock); + return 0; + } + + /* Suspend ourselves, then try again */ + enqueue (&rwlock->__rw_write_waiting, self); + __pthread_unlock (&rwlock->__rw_lock); + suspend (self); /* This is not a cancellation point */ + } +} + + +int +pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock) +{ + int result = EBUSY; + + __pthread_lock (&rwlock->__rw_lock, NULL); + if (rwlock->__rw_readers == 0 && rwlock->__rw_writer == NULL) + { + rwlock->__rw_writer = thread_self (); + result = 0; + } + __pthread_unlock (&rwlock->__rw_lock); + + return result; +} + + +int +pthread_rwlock_unlock (pthread_rwlock_t *rwlock) +{ + pthread_descr torestart; + pthread_descr th; + + __pthread_lock (&rwlock->__rw_lock, NULL); + if (rwlock->__rw_writer != NULL) + { + /* Unlocking a write lock. */ + if (rwlock->__rw_writer != thread_self ()) + { + __pthread_unlock (&rwlock->__rw_lock); + return EPERM; + } + rwlock->__rw_writer = NULL; + + if (rwlock->__rw_kind == PTHREAD_RWLOCK_PREFER_READER_NP + || (th = dequeue (&rwlock->__rw_write_waiting)) == NULL) + { + /* Restart all waiting readers. */ + torestart = rwlock->__rw_read_waiting; + rwlock->__rw_read_waiting = NULL; + __pthread_unlock (&rwlock->__rw_lock); + while ((th = dequeue (&torestart)) != NULL) + restart (th); + } + else + { + /* Restart one waiting writer. */ + __pthread_unlock (&rwlock->__rw_lock); + restart (th); + } + } + else + { + /* Unlocking a read lock. */ + if (rwlock->__rw_readers == 0) + { + __pthread_unlock (&rwlock->__rw_lock); + return EPERM; + } + + --rwlock->__rw_readers; + if (rwlock->__rw_readers == 0) + /* Restart one waiting writer, if any. */ + th = dequeue (&rwlock->__rw_write_waiting); + else + th = NULL; + + __pthread_unlock (&rwlock->__rw_lock); + if (th != NULL) + restart (th); + + /* Recursive lock fixup */ + + if (rwlock->__rw_kind == PTHREAD_RWLOCK_PREFER_WRITER_NP) + { + pthread_descr self = thread_self(); + pthread_readlock_info *victim = rwlock_remove_from_list(self, rwlock); + + if (victim != NULL) + { + if (victim->pr_lock_count == 0) + { + victim->pr_next = self->p_readlock_free; + self->p_readlock_free = victim; + } + } + else + { + if (self->p_untracked_readlock_count > 0) + self->p_untracked_readlock_count--; + } + } + } + + return 0; +} + + + +int +pthread_rwlockattr_init (pthread_rwlockattr_t *attr) +{ + attr->__lockkind = 0; + attr->__pshared = 0; + + return 0; +} + + +int +pthread_rwlockattr_destroy (pthread_rwlockattr_t *attr attribute_unused) +{ + return 0; +} + + +int +pthread_rwlockattr_getpshared (const pthread_rwlockattr_t *attr, int *pshared) +{ + *pshared = attr->__pshared; + return 0; +} + + +int +pthread_rwlockattr_setpshared (pthread_rwlockattr_t *attr, int pshared) +{ + if (pshared != PTHREAD_PROCESS_PRIVATE && pshared != PTHREAD_PROCESS_SHARED) + return EINVAL; + + attr->__pshared = pshared; + + return 0; +} + + +int +pthread_rwlockattr_getkind_np (const pthread_rwlockattr_t *attr, int *pref) +{ + *pref = attr->__lockkind; + return 0; +} + + +int +pthread_rwlockattr_setkind_np (pthread_rwlockattr_t *attr, int pref) +{ + if (pref != PTHREAD_RWLOCK_PREFER_READER_NP + && pref != PTHREAD_RWLOCK_PREFER_WRITER_NP + && pref != PTHREAD_RWLOCK_DEFAULT_NP) + return EINVAL; + + attr->__lockkind = pref; + + return 0; +} |