SDL 3.0
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Functions to provide thread synchronization primitives. More...
#include <SDL3/SDL_stdinc.h>
#include <SDL3/SDL_error.h>
#include <SDL3/SDL_begin_code.h>
#include <SDL3/SDL_close_code.h>
Go to the source code of this file.
Read/write lock functions | |
#define | SDL_RWLOCK_TIMEDOUT SDL_MUTEX_TIMEDOUT |
typedef struct SDL_RWLock | SDL_RWLock |
int | rwlock |
SDL_RWLock * | SDL_CreateRWLock (void) |
int | SDL_LockRWLockForReading (SDL_RWLock *rwlock) SDL_ACQUIRE_SHARED(rwlock) |
int | SDL_LockRWLockForWriting (SDL_RWLock *rwlock) SDL_ACQUIRE(rwlock) |
int | SDL_TryLockRWLockForReading (SDL_RWLock *rwlock) SDL_TRY_ACQUIRE_SHARED(0 |
int | SDL_TryLockRWLockForWriting (SDL_RWLock *rwlock) SDL_TRY_ACQUIRE(0 |
int | SDL_UnlockRWLock (SDL_RWLock *rwlock) SDL_RELEASE_SHARED(rwlock) |
void | SDL_DestroyRWLock (SDL_RWLock *rwlock) |
Mutex functions | |
typedef struct SDL_Mutex | SDL_Mutex |
int | mutex |
SDL_Mutex * | SDL_CreateMutex (void) |
int | SDL_LockMutex (SDL_Mutex *mutex) SDL_ACQUIRE(mutex) |
int | SDL_TryLockMutex (SDL_Mutex *mutex) SDL_TRY_ACQUIRE(0 |
int | SDL_UnlockMutex (SDL_Mutex *mutex) SDL_RELEASE(mutex) |
void | SDL_DestroyMutex (SDL_Mutex *mutex) |
Semaphore functions | |
typedef struct SDL_Semaphore | SDL_Semaphore |
SDL_Semaphore * | SDL_CreateSemaphore (Uint32 initial_value) |
void | SDL_DestroySemaphore (SDL_Semaphore *sem) |
int | SDL_WaitSemaphore (SDL_Semaphore *sem) |
int | SDL_TryWaitSemaphore (SDL_Semaphore *sem) |
int | SDL_WaitSemaphoreTimeout (SDL_Semaphore *sem, Sint32 timeoutMS) |
int | SDL_PostSemaphore (SDL_Semaphore *sem) |
Uint32 | SDL_GetSemaphoreValue (SDL_Semaphore *sem) |
Condition variable functions | |
typedef struct SDL_Condition | SDL_Condition |
SDL_Condition * | SDL_CreateCondition (void) |
void | SDL_DestroyCondition (SDL_Condition *cond) |
int | SDL_SignalCondition (SDL_Condition *cond) |
int | SDL_BroadcastCondition (SDL_Condition *cond) |
int | SDL_WaitCondition (SDL_Condition *cond, SDL_Mutex *mutex) |
int | SDL_WaitConditionTimeout (SDL_Condition *cond, SDL_Mutex *mutex, Sint32 timeoutMS) |
Functions to provide thread synchronization primitives.
Definition in file SDL_mutex.h.
#define SDL_ACQUIRE | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquire_capability(x)) |
Definition at line 73 of file SDL_mutex.h.
#define SDL_ACQUIRE_SHARED | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquire_shared_capability(x)) |
Definition at line 76 of file SDL_mutex.h.
#define SDL_ACQUIRED_AFTER | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(x)) |
Definition at line 64 of file SDL_mutex.h.
#define SDL_ACQUIRED_BEFORE | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(x)) |
Definition at line 61 of file SDL_mutex.h.
#define SDL_ASSERT_CAPABILITY | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(assert_capability(x)) |
Definition at line 97 of file SDL_mutex.h.
#define SDL_ASSERT_SHARED_CAPABILITY | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(assert_shared_capability(x)) |
Definition at line 100 of file SDL_mutex.h.
#define SDL_CAPABILITY | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(capability(x)) |
Definition at line 49 of file SDL_mutex.h.
#define SDL_EXCLUDES | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(x)) |
Definition at line 94 of file SDL_mutex.h.
#define SDL_GUARDED_BY | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x)) |
Definition at line 55 of file SDL_mutex.h.
#define SDL_MUTEX_MAXWAIT -1 |
This is the timeout value which corresponds to never time out.
Definition at line 127 of file SDL_mutex.h.
#define SDL_MUTEX_TIMEDOUT 1 |
Synchronization functions which can time out return this value if they time out.
Definition at line 122 of file SDL_mutex.h.
#define SDL_NO_THREAD_SAFETY_ANALYSIS SDL_THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis) |
Definition at line 106 of file SDL_mutex.h.
#define SDL_PT_GUARDED_BY | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x)) |
Definition at line 58 of file SDL_mutex.h.
#define SDL_RELEASE | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(release_capability(x)) |
Definition at line 79 of file SDL_mutex.h.
#define SDL_RELEASE_GENERIC | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(release_generic_capability(x)) |
Definition at line 85 of file SDL_mutex.h.
#define SDL_RELEASE_SHARED | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(release_shared_capability(x)) |
Definition at line 82 of file SDL_mutex.h.
#define SDL_REQUIRES | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(requires_capability(x)) |
Definition at line 67 of file SDL_mutex.h.
#define SDL_REQUIRES_SHARED | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(requires_shared_capability(x)) |
Definition at line 70 of file SDL_mutex.h.
#define SDL_RETURN_CAPABILITY | ( | x | ) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x)) |
Definition at line 103 of file SDL_mutex.h.
#define SDL_RWLOCK_TIMEDOUT SDL_MUTEX_TIMEDOUT |
Definition at line 256 of file SDL_mutex.h.
#define SDL_SCOPED_CAPABILITY SDL_THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable) |
Definition at line 52 of file SDL_mutex.h.
#define SDL_THREAD_ANNOTATION_ATTRIBUTE__ | ( | x | ) | /* no-op */ |
Definition at line 46 of file SDL_mutex.h.
#define SDL_TRY_ACQUIRE | ( | x, | |
y | |||
) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(try_acquire_capability(x, y)) |
Definition at line 88 of file SDL_mutex.h.
#define SDL_TRY_ACQUIRE_SHARED | ( | x, | |
y | |||
) | SDL_THREAD_ANNOTATION_ATTRIBUTE__(try_acquire_shared_capability(x, y)) |
Definition at line 91 of file SDL_mutex.h.
typedef struct SDL_Condition SDL_Condition |
Definition at line 631 of file SDL_mutex.h.
Definition at line 137 of file SDL_mutex.h.
typedef struct SDL_RWLock SDL_RWLock |
Definition at line 250 of file SDL_mutex.h.
typedef struct SDL_Semaphore SDL_Semaphore |
Definition at line 470 of file SDL_mutex.h.
int SDL_BroadcastCondition | ( | SDL_Condition * | cond | ) |
Restart all threads that are waiting on the condition variable.
cond | the condition variable to signal |
SDL_Condition * SDL_CreateCondition | ( | void | ) |
Create a condition variable.
SDL_Mutex * SDL_CreateMutex | ( | void | ) |
Create a new mutex.
All newly-created mutexes begin in the unlocked state.
Calls to SDL_LockMutex() will not return while the mutex is locked by another thread. See SDL_TryLockMutex() to attempt to lock without blocking.
SDL mutexes are reentrant.
SDL_RWLock * SDL_CreateRWLock | ( | void | ) |
Create a new read/write lock.
A read/write lock is useful for situations where you have multiple threads trying to access a resource that is rarely updated. All threads requesting a read-only lock will be allowed to run in parallel; if a thread requests a write lock, it will be provided exclusive access. This makes it safe for multiple threads to use a resource at the same time if they promise not to change it, and when it has to be changed, the rwlock will serve as a gateway to make sure those changes can be made safely.
In the right situation, a rwlock can be more efficient than a mutex, which only lets a single thread proceed at a time, even if it won't be modifying the data.
All newly-created read/write locks begin in the unlocked state.
Calls to SDL_LockRWLockForReading() and SDL_LockRWLockForWriting will not return while the rwlock is locked for writing by another thread. See SDL_TryLockRWLockForReading() and SDL_TryLockRWLockForWriting() to attempt to lock without blocking.
SDL read/write locks are only recursive for read-only locks! They are not guaranteed to be fair, or provide access in a FIFO manner! They are not guaranteed to favor writers. You may not lock a rwlock for both read-only and write access at the same time from the same thread (so you can't promote your read-only lock to a write lock without unlocking first).
SDL_Semaphore * SDL_CreateSemaphore | ( | Uint32 | initial_value | ) |
Create a semaphore.
This function creates a new semaphore and initializes it with the value initial_value
. Each wait operation on the semaphore will atomically decrement the semaphore value and potentially block if the semaphore value is 0. Each post operation will atomically increment the semaphore value and wake waiting threads and allow them to retry the wait operation.
initial_value | the starting value of the semaphore |
void SDL_DestroyCondition | ( | SDL_Condition * | cond | ) |
Destroy a condition variable.
cond | the condition variable to destroy |
void SDL_DestroyMutex | ( | SDL_Mutex * | mutex | ) |
Destroy a mutex created with SDL_CreateMutex().
This function must be called on any mutex that is no longer needed. Failure to destroy a mutex will result in a system memory or resource leak. While it is safe to destroy a mutex that is unlocked, it is not safe to attempt to destroy a locked mutex, and may result in undefined behavior depending on the platform.
mutex | the mutex to destroy |
void SDL_DestroyRWLock | ( | SDL_RWLock * | rwlock | ) |
Destroy a read/write lock created with SDL_CreateRWLock().
This function must be called on any read/write lock that is no longer needed. Failure to destroy a rwlock will result in a system memory or resource leak. While it is safe to destroy a rwlock that is unlocked, it is not safe to attempt to destroy a locked rwlock, and may result in undefined behavior depending on the platform.
rwlock | the rwlock to destroy |
void SDL_DestroySemaphore | ( | SDL_Semaphore * | sem | ) |
Destroy a semaphore.
It is not safe to destroy a semaphore if there are threads currently waiting on it.
sem | the semaphore to destroy |
Uint32 SDL_GetSemaphoreValue | ( | SDL_Semaphore * | sem | ) |
Get the current value of a semaphore.
sem | the semaphore to query |
int SDL_LockMutex | ( | SDL_Mutex * | mutex | ) |
Lock the mutex.
This will block until the mutex is available, which is to say it is in the unlocked state and the OS has chosen the caller as the next thread to lock it. Of all threads waiting to lock the mutex, only one may do so at a time.
It is legal for the owning thread to lock an already-locked mutex. It must unlock it the same number of times before it is actually made available for other threads in the system (this is known as a "recursive mutex").
mutex | the mutex to lock |
int SDL_LockRWLockForReading | ( | SDL_RWLock * | rwlock | ) |
Lock the read/write lock for read only operations.
This will block until the rwlock is available, which is to say it is not locked for writing by any other thread. Of all threads waiting to lock the rwlock, all may do so at the same time as long as they are requesting read-only access; if a thread wants to lock for writing, only one may do so at a time, and no other threads, read-only or not, may hold the lock at the same time.
It is legal for the owning thread to lock an already-locked rwlock for reading. It must unlock it the same number of times before it is actually made available for other threads in the system (this is known as a "recursive rwlock").
Note that locking for writing is not recursive (this is only available to read-only locks).
It is illegal to request a read-only lock from a thread that already holds the write lock. Doing so results in undefined behavior. Unlock the write lock before requesting a read-only lock. (But, of course, if you have the write lock, you don't need further locks to read in any case.)
rwlock | the read/write lock to lock |
int SDL_LockRWLockForWriting | ( | SDL_RWLock * | rwlock | ) |
Lock the read/write lock for write operations.
This will block until the rwlock is available, which is to say it is not locked for reading or writing by any other thread. Only one thread may hold the lock when it requests write access; all other threads, whether they also want to write or only want read-only access, must wait until the writer thread has released the lock.
It is illegal for the owning thread to lock an already-locked rwlock for writing (read-only may be locked recursively, writing can not). Doing so results in undefined behavior.
It is illegal to request a write lock from a thread that already holds a read-only lock. Doing so results in undefined behavior. Unlock the read-only lock before requesting a write lock.
rwlock | the read/write lock to lock |
int SDL_PostSemaphore | ( | SDL_Semaphore * | sem | ) |
Atomically increment a semaphore's value and wake waiting threads.
sem | the semaphore to increment |
int SDL_SignalCondition | ( | SDL_Condition * | cond | ) |
Restart one of the threads that are waiting on the condition variable.
cond | the condition variable to signal |
int SDL_TryLockMutex | ( | SDL_Mutex * | mutex | ) |
Try to lock a mutex without blocking.
This works just like SDL_LockMutex(), but if the mutex is not available, this function returns SDL_MUTEX_TIMEDOUT
immediately.
This technique is useful if you need exclusive access to a resource but don't want to wait for it, and will return to it to try again later.
mutex | the mutex to try to lock |
SDL_MUTEX_TIMEDOUT
, or -1 on error; call SDL_GetError() for more information.int SDL_TryLockRWLockForReading | ( | SDL_RWLock * | rwlock | ) |
Try to lock a read/write lock for reading without blocking.
This works just like SDL_LockRWLockForReading(), but if the rwlock is not available, then this function returns SDL_RWLOCK_TIMEDOUT
immediately.
This technique is useful if you need access to a resource but don't want to wait for it, and will return to it to try again later.
Trying to lock for read-only access can succeed if other threads are holding read-only locks, as this won't prevent access.
rwlock | the rwlock to try to lock |
SDL_RWLOCK_TIMEDOUT
, or -1 on error; call SDL_GetError() for more information.int SDL_TryLockRWLockForWriting | ( | SDL_RWLock * | rwlock | ) |
Try to lock a read/write lock for writing without blocking.
This works just like SDL_LockRWLockForWriting(), but if the rwlock is not available, this function returns SDL_RWLOCK_TIMEDOUT
immediately.
This technique is useful if you need exclusive access to a resource but don't want to wait for it, and will return to it to try again later.
It is illegal for the owning thread to lock an already-locked rwlock for writing (read-only may be locked recursively, writing can not). Doing so results in undefined behavior.
It is illegal to request a write lock from a thread that already holds a read-only lock. Doing so results in undefined behavior. Unlock the read-only lock before requesting a write lock.
rwlock | the rwlock to try to lock |
SDL_RWLOCK_TIMEDOUT
, or -1 on error; call SDL_GetError() for more information.int SDL_TryWaitSemaphore | ( | SDL_Semaphore * | sem | ) |
See if a semaphore has a positive value and decrement it if it does.
This function checks to see if the semaphore pointed to by sem
has a positive value and atomically decrements the semaphore value if it does. If the semaphore doesn't have a positive value, the function immediately returns SDL_MUTEX_TIMEDOUT.
sem | the semaphore to wait on |
SDL_MUTEX_TIMEDOUT
if the wait would block, or a negative error code on failure; call SDL_GetError() for more information.int SDL_UnlockMutex | ( | SDL_Mutex * | mutex | ) |
Unlock the mutex.
It is legal for the owning thread to lock an already-locked mutex. It must unlock it the same number of times before it is actually made available for other threads in the system (this is known as a "recursive mutex").
It is illegal to unlock a mutex that has not been locked by the current thread, and doing so results in undefined behavior.
mutex | the mutex to unlock. |
int SDL_UnlockRWLock | ( | SDL_RWLock * | rwlock | ) |
Unlock the read/write lock.
Use this function to unlock the rwlock, whether it was locked for read-only or write operations.
It is legal for the owning thread to lock an already-locked read-only lock. It must unlock it the same number of times before it is actually made available for other threads in the system (this is known as a "recursive rwlock").
It is illegal to unlock a rwlock that has not been locked by the current thread, and doing so results in undefined behavior.
rwlock | the rwlock to unlock. |
int SDL_WaitCondition | ( | SDL_Condition * | cond, |
SDL_Mutex * | mutex | ||
) |
Wait until a condition variable is signaled.
This function unlocks the specified mutex
and waits for another thread to call SDL_SignalCondition() or SDL_BroadcastCondition() on the condition variable cond
. Once the condition variable is signaled, the mutex is re-locked and the function returns.
The mutex must be locked before calling this function. Locking the mutex recursively (more than once) is not supported and leads to undefined behavior.
This function is the equivalent of calling SDL_WaitConditionTimeout() with a time length of SDL_MUTEX_MAXWAIT
.
cond | the condition variable to wait on |
mutex | the mutex used to coordinate thread access |
int SDL_WaitConditionTimeout | ( | SDL_Condition * | cond, |
SDL_Mutex * | mutex, | ||
Sint32 | timeoutMS | ||
) |
Wait until a condition variable is signaled or a certain time has passed.
This function unlocks the specified mutex
and waits for another thread to call SDL_SignalCondition() or SDL_BroadcastCondition() on the condition variable cond
, or for the specified time to elapse. Once the condition variable is signaled or the time elapsed, the mutex is re-locked and the function returns.
The mutex must be locked before calling this function. Locking the mutex recursively (more than once) is not supported and leads to undefined behavior.
cond | the condition variable to wait on |
mutex | the mutex used to coordinate thread access |
timeoutMS | the maximum time to wait, in milliseconds, or SDL_MUTEX_MAXWAIT to wait indefinitely |
SDL_MUTEX_TIMEDOUT
if the condition is not signaled in the allotted time, or a negative error code on failure; call SDL_GetError() for more information.int SDL_WaitSemaphore | ( | SDL_Semaphore * | sem | ) |
Wait until a semaphore has a positive value and then decrements it.
This function suspends the calling thread until either the semaphore pointed to by sem
has a positive value or the call is interrupted by a signal or error. If the call is successful it will atomically decrement the semaphore value.
This function is the equivalent of calling SDL_WaitSemaphoreTimeout() with a time length of SDL_MUTEX_MAXWAIT
.
sem | the semaphore wait on |
int SDL_WaitSemaphoreTimeout | ( | SDL_Semaphore * | sem, |
Sint32 | timeoutMS | ||
) |
Wait until a semaphore has a positive value and then decrements it.
This function suspends the calling thread until either the semaphore pointed to by sem
has a positive value, the call is interrupted by a signal or error, or the specified time has elapsed. If the call is successful it will atomically decrement the semaphore value.
sem | the semaphore to wait on |
timeoutMS | the length of the timeout, in milliseconds |
SDL_MUTEX_TIMEDOUT
if the wait does not succeed in the allotted time, or a negative error code on failure; call SDL_GetError() for more information.int mutex |
Definition at line 200 of file SDL_mutex.h.
int rwlock |
Definition at line 384 of file SDL_mutex.h.