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spa: add locking to the loop

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We can add a PTHREAD_PRIO_INHERIT lock to the loop to protect the
callbacks and then use this to update shared data in an RT-safe way.

This can avoid some invoke calls that require a context switch but
also due to the nature of epoll cause locking in the kernel with non-RT
guarantees.

Because we use PRIO_INHERIT, the code executed in the lock must not use
any RT-unsafe functions.
This commit is contained in:
Wim Taymans 2025-03-10 09:13:52 +01:00
parent d258892392
commit 65cbbf1a02
2 changed files with 152 additions and 12 deletions
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71
spa/include/spa/support/loop.h
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@ -38,7 +38,7 @@ extern "C" {
struct spa_loop { struct spa_interface iface; };
#define SPA_TYPE_INTERFACE_LoopControl SPA_TYPE_INFO_INTERFACE_BASE "LoopControl"
#define SPA_VERSION_LOOP_CONTROL 1
#define SPA_VERSION_LOOP_CONTROL 2
struct spa_loop_control { struct spa_interface iface; };
#define SPA_TYPE_INTERFACE_LoopUtils SPA_TYPE_INFO_INTERFACE_BASE "LoopUtils"
@ -213,7 +213,7 @@ SPA_API_LOOP void spa_loop_control_hook_after(struct spa_hook_list *l)
struct spa_loop_control_methods {
/* the version of this structure. This can be used to expand this
* structure in the future */
#define SPA_VERSION_LOOP_CONTROL_METHODS 1
#define SPA_VERSION_LOOP_CONTROL_METHODS 2
uint32_t version;
/** get the loop fd
@ -275,6 +275,46 @@ struct spa_loop_control_methods {
* returns 1 on success, 0 or negative errno value on error.
*/
int (*check) (void *object);
/** Lock the loop.
* This will ensure the loop is not in the process of dispatching
* callbacks. Since version 2:2
*
* \param[in] object the control
* \return 0 on success or a negative return value on error.
*/
int (*lock) (void *object);
/** Unlock the loop.
* Unlocks the loop again so that callbacks can be dispatched
* again. Since version 2:2
*
* \param[in] object the control
* \return 0 on success or a negative return value on error.
*/
int (*unlock) (void *object);
/** get the absolute time
* Get the current time with \ref timeout that can be used in wait.
* Since version 2:2
*/
int (*get_time) (void *object, struct timespec *abstime, int64_t timeout);
/** Wait for a signal
* Wait until a thread performs signal. Since version 2:2
*
* \param[in] object the control
* \param[in] abstime the maximum time to wait for the signal or NULL
* \return 0 on success or a negative return value on error.
*/
int (*wait) (void *object, struct timespec *abstime);
/** Signal waiters
* Wake up all thread blocked in wait. Since version 2:2
*
* \param[in] object the control
* \return 0 on success or a negative return value on error.
*/
int (*signal) (void *object);
};
SPA_API_LOOP int spa_loop_control_get_fd(struct spa_loop_control *object)
@ -314,6 +354,33 @@ SPA_API_LOOP int spa_loop_control_check(struct spa_loop_control *object)
return spa_api_method_r(int, -ENOTSUP,
spa_loop_control, &object->iface, check, 1);
}
SPA_API_LOOP int spa_loop_control_lock(struct spa_loop_control *object)
{
return spa_api_method_r(int, -ENOTSUP,
spa_loop_control, &object->iface, lock, 2);
}
SPA_API_LOOP int spa_loop_control_unlock(struct spa_loop_control *object)
{
return spa_api_method_r(int, -ENOTSUP,
spa_loop_control, &object->iface, unlock, 2);
}
SPA_API_LOOP int spa_loop_control_get_time(struct spa_loop_control *object,
struct timespec *abstime, int64_t timeout)
{
return spa_api_method_r(int, -ENOTSUP,
spa_loop_control, &object->iface, get_time, 2, abstime, timeout);
}
SPA_API_LOOP int spa_loop_control_wait(struct spa_loop_control *object,
struct timespec *abstime)
{
return spa_api_method_r(int, -ENOTSUP,
spa_loop_control, &object->iface, wait, 2, abstime);
}
SPA_API_LOOP int spa_loop_control_signal(struct spa_loop_control *object)
{
return spa_api_method_r(int, -ENOTSUP,
spa_loop_control, &object->iface, signal, 2);
}
typedef void (*spa_source_io_func_t) (void *data, int fd, uint32_t mask);
typedef void (*spa_source_idle_func_t) (void *data);