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Added recursive read_lock support to our own implementation of rwlock_t.

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This commit is contained in:
Tobias Brunner 2012-01-21 16:11:28 +01:00
parent 0e474f9148
commit 4d21000cf7
1 changed files with 35 additions and 4 deletions
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39
src/libstrongswan/threading/rwlock.c
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@ -1,5 +1,5 @@
/* /*
* Copyright (C) 2008-2009 Tobias Brunner * Copyright (C) 2008-2012 Tobias Brunner
* Copyright (C) 2008 Martin Willi * Copyright (C) 2008 Martin Willi
* Hochschule fuer Technik Rapperswil * Hochschule fuer Technik Rapperswil
* *
@ -23,6 +23,7 @@
#include "rwlock.h" #include "rwlock.h"
#include "condvar.h" #include "condvar.h"
#include "mutex.h" #include "mutex.h"
#include "thread_value.h"
#include "lock_profiler.h" #include "lock_profiler.h"
typedef struct private_rwlock_t private_rwlock_t; typedef struct private_rwlock_t private_rwlock_t;
@ -61,6 +62,11 @@ struct private_rwlock_t {
*/ */
condvar_t *readers; condvar_t *readers;
/**
* thread local value to keep track whether the current thread is a reader
*/
thread_value_t *is_reading;
/** /**
* number of waiting writers * number of waiting writers
*/ */
@ -189,14 +195,24 @@ rwlock_t *rwlock_create(rwlock_type_t type)
* of incoming readers. Reader starvation is not prevented (this could happen * of incoming readers. Reader starvation is not prevented (this could happen
* if there are more writers than readers). * if there are more writers than readers).
* *
* The implementation does not support recursive locking and readers must not * The implementation supports recursive locking of the read lock but not of
* acquire the lock exclusively at the same time and vice-versa (this is not * the write lock. Readers must not acquire the lock exclusively at the same
* checked or enforced so behave yourself to prevent deadlocks). * time and vice-versa (this is not checked or enforced so behave yourself to
* prevent deadlocks).
*/ */
METHOD(rwlock_t, read_lock, void, METHOD(rwlock_t, read_lock, void,
private_rwlock_t *this) private_rwlock_t *this)
{ {
uintptr_t reading;
reading = (uintptr_t)this->is_reading->get(this->is_reading);
if (reading > 0)
{ /* we allow readers to acquire the lock recursively */
this->is_reading->set(this->is_reading, (void*)(reading + 1));
return;
}
profiler_start(&this->profile); profiler_start(&this->profile);
this->mutex->lock(this->mutex); this->mutex->lock(this->mutex);
while (this->writer || this->waiting_writers) while (this->writer || this->waiting_writers)
@ -206,6 +222,8 @@ METHOD(rwlock_t, read_lock, void,
this->reader_count++; this->reader_count++;
profiler_end(&this->profile); profiler_end(&this->profile);
this->mutex->unlock(this->mutex); this->mutex->unlock(this->mutex);
this->is_reading->set(this->is_reading, (void*)1);
} }
METHOD(rwlock_t, write_lock, void, METHOD(rwlock_t, write_lock, void,
@ -241,6 +259,15 @@ METHOD(rwlock_t, try_write_lock, bool,
METHOD(rwlock_t, unlock, void, METHOD(rwlock_t, unlock, void,
private_rwlock_t *this) private_rwlock_t *this)
{ {
uintptr_t reading;
reading = (uintptr_t)this->is_reading->get(this->is_reading);
if (reading > 1)
{ /* readers have to unlock an equal number of times */
this->is_reading->set(this->is_reading, (void*)(reading - 1));
return;
}
this->mutex->lock(this->mutex); this->mutex->lock(this->mutex);
if (this->writer == pthread_self()) if (this->writer == pthread_self())
{ {
@ -263,6 +290,8 @@ METHOD(rwlock_t, unlock, void,
} }
} }
this->mutex->unlock(this->mutex); this->mutex->unlock(this->mutex);
this->is_reading->set(this->is_reading, NULL);
} }
METHOD(rwlock_t, destroy, void, METHOD(rwlock_t, destroy, void,
@ -271,6 +300,7 @@ METHOD(rwlock_t, destroy, void,
this->mutex->destroy(this->mutex); this->mutex->destroy(this->mutex);
this->writers->destroy(this->writers); this->writers->destroy(this->writers);
this->readers->destroy(this->readers); this->readers->destroy(this->readers);
this->is_reading->destroy(this->is_reading);
profiler_cleanup(&this->profile); profiler_cleanup(&this->profile);
free(this); free(this);
} }
@ -298,6 +328,7 @@ rwlock_t *rwlock_create(rwlock_type_t type)
.mutex = mutex_create(MUTEX_TYPE_DEFAULT), .mutex = mutex_create(MUTEX_TYPE_DEFAULT),
.writers = condvar_create(CONDVAR_TYPE_DEFAULT), .writers = condvar_create(CONDVAR_TYPE_DEFAULT),
.readers = condvar_create(CONDVAR_TYPE_DEFAULT), .readers = condvar_create(CONDVAR_TYPE_DEFAULT),
.is_reading = thread_value_create(NULL),
); );
profiler_init(&this->profile); profiler_init(&this->profile);