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incubator-nuttx
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shced:sem: replace mutex with spinlock 

The overhead of spinlok is less than mutext (mutex need to call
enter_critical section.)
After this patch, `down_write_trylock` and `down_read_trylock` can be
use in interrupt context.

The instruction is protected with mutex only one instruction so using
spinlock is better.

Signed-off-by: TaiJu Wu <tjwu1217@gmail.com>
This commit is contained in:
TaiJu Wu 2024-02-26 01:45:21 +00:00 committed by Xiang Xiao
parent a7389c0057
commit 23d65cb97f
2 changed files with 28 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
include/nuttx/rwsem.h
View File

@ -25,7 +25,8 @@
* Included Files
****************************************************************************/
#include <nuttx/mutex.h>
#include <nuttx/semaphore.h>
#include <nuttx/spinlock.h>
/****************************************************************************
* Public Type Definitions
@ -33,11 +34,11 @@
typedef struct
{
mutex_t protected; /* Protecting Locks for Read/Write Locked Tables */
sem_t waiting; /* Reader/writer Waiting queue */
int waiter; /* Waiter Count */
int writer; /* Writer Count */
int reader; /* Reader Count */
spinlock_t protected;
sem_t waiting;
int waiter;
int writer;
int reader;
} rw_semaphore_t;
/****************************************************************************

46
sched/semaphore/sem_rw.c
View File

@ -23,6 +23,8 @@
****************************************************************************/
#include <nuttx/rwsem.h>
#include <nuttx/irq.h>
#include <assert.h>
/****************************************************************************
* Private Functions
@ -61,11 +63,11 @@ static inline void up_wait(FAR rw_semaphore_t *rwsem)
int down_read_trylock(FAR rw_semaphore_t *rwsem)
{
nxmutex_lock(&rwsem->protected);
irqstate_t flags = spin_lock_irqsave(&rwsem->protected);
if (rwsem->writer > 0)
{
nxmutex_unlock(&rwsem->protected);
spin_unlock_irqrestore(&rwsem->protected, flags);
return 0;
}
@ -75,7 +77,7 @@ int down_read_trylock(FAR rw_semaphore_t *rwsem)
rwsem->reader++;
nxmutex_unlock(&rwsem->protected);
spin_unlock_irqrestore(&rwsem->protected, flags);
return 1;
}
@ -97,14 +99,14 @@ void down_read(FAR rw_semaphore_t *rwsem)
* block and wait for the write-lock to be unlocked.
*/
nxmutex_lock(&rwsem->protected);
irqstate_t flags = spin_lock_irqsave(&rwsem->protected);
while (rwsem->writer > 0)
{
rwsem->waiter++;
nxmutex_unlock(&rwsem->protected);
spin_unlock_irqrestore(&rwsem->protected, flags);
nxsem_wait(&rwsem->waiting);
nxmutex_lock(&rwsem->protected);
flags = spin_lock_irqsave(&rwsem->protected);
rwsem->waiter--;
}
@ -114,7 +116,7 @@ void down_read(FAR rw_semaphore_t *rwsem)
rwsem->reader++;
nxmutex_unlock(&rwsem->protected);
spin_unlock_irqrestore(&rwsem->protected, flags);
}
/****************************************************************************
@ -130,7 +132,7 @@ void down_read(FAR rw_semaphore_t *rwsem)
void up_read(FAR rw_semaphore_t *rwsem)
{
nxmutex_lock(&rwsem->protected);
irqstate_t flags = spin_lock_irqsave(&rwsem->protected);
DEBUGASSERT(rwsem->reader > 0);
@ -141,7 +143,7 @@ void up_read(FAR rw_semaphore_t *rwsem)
up_wait(rwsem);
}
nxmutex_unlock(&rwsem->protected);
spin_unlock_irqrestore(&rwsem->protected, flags);
}
/****************************************************************************
@ -160,11 +162,11 @@ void up_read(FAR rw_semaphore_t *rwsem)
int down_write_trylock(FAR rw_semaphore_t *rwsem)
{
nxmutex_lock(&rwsem->protected);
irqstate_t flags = spin_lock_irqsave(&rwsem->protected);
if (rwsem->writer > 0 || rwsem->reader > 0)
{
nxmutex_unlock(&rwsem->protected);
spin_unlock_irqrestore(&rwsem->protected, flags);
return 0;
}
@ -172,7 +174,7 @@ int down_write_trylock(FAR rw_semaphore_t *rwsem)
rwsem->writer++;
nxmutex_unlock(&rwsem->protected);
spin_unlock_irqrestore(&rwsem->protected, flags);
return 1;
}
@ -190,14 +192,14 @@ int down_write_trylock(FAR rw_semaphore_t *rwsem)
void down_write(FAR rw_semaphore_t *rwsem)
{
nxmutex_lock(&rwsem->protected);
irqstate_t flags = spin_lock_irqsave(&rwsem->protected);
while (rwsem->reader > 0 || rwsem->writer > 0)
{
rwsem->waiter++;
nxmutex_unlock(&rwsem->protected);
spin_unlock_irqrestore(&rwsem->protected, flags);
nxsem_wait(&rwsem->waiting);
nxmutex_lock(&rwsem->protected);
flags = spin_lock_irqsave(&rwsem->protected);
rwsem->waiter--;
}
@ -205,7 +207,7 @@ void down_write(FAR rw_semaphore_t *rwsem)
rwsem->writer++;
nxmutex_unlock(&rwsem->protected);
spin_unlock_irqrestore(&rwsem->protected, flags);
}
/****************************************************************************
@ -221,7 +223,7 @@ void down_write(FAR rw_semaphore_t *rwsem)
void up_write(FAR rw_semaphore_t *rwsem)
{
nxmutex_lock(&rwsem->protected);
irqstate_t flags = spin_lock_irqsave(&rwsem->protected);
DEBUGASSERT(rwsem->writer > 0);
@ -229,7 +231,7 @@ void up_write(FAR rw_semaphore_t *rwsem)
up_wait(rwsem);
nxmutex_unlock(&rwsem->protected);
spin_unlock_irqrestore(&rwsem->protected, flags);
}
/****************************************************************************
@ -253,16 +255,11 @@ int init_rwsem(FAR rw_semaphore_t *rwsem)
/* Initialize structure information */
ret = nxmutex_init(&rwsem->protected);
if (ret < 0)
{
return ret;
}
spin_lock_init(&rwsem->protected);
ret = nxsem_init(&rwsem->waiting, 0, 0);
if (ret < 0)
{
nxmutex_destroy(&rwsem->protected);
return ret;
}
@ -292,6 +289,5 @@ void destroy_rwsem(FAR rw_semaphore_t *rwsem)
DEBUGASSERT(rwsem->waiter == 0 && rwsem->reader == 0 &&
rwsem->writer == 0);
nxmutex_destroy(&rwsem->protected);
nxsem_destroy(&rwsem->waiting);
}