QP/C  7.4.0-rc.2
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QXMutex Class Reference

Blocking Mutex of the QXK preemptive kernel. More...

#include "qxk.h"

Public Member Functions

void QXMutex_init (QXMutex *const me, QPrioSpec const prioSpec)
 
bool QXMutex_lock (QXMutex *const me, QTimeEvtCtr const nTicks)
 
bool QXMutex_tryLock (QXMutex *const me)
 
void QXMutex_unlock (QXMutex *const me)
 

Private Attributes

QActive ao
 
QPSet waitSet
 

Detailed Description

Blocking Mutex of the QXK preemptive kernel.

Description
QXMutex is a blocking mutual exclusion mechanism that can also apply the priority-ceiling protocol to avoid unbounded priority inversion (if initialized with a non-zero ceiling priority, see QXMutex_init()). In that case, QXMutex requires its own unique QP priority level, which cannot be used by any thread or any other QXMutex.

If initialized with preemption-ceiling of zero, QXMutex does not use the priority-ceiling protocol and does not require a unique QP priority (see QXMutex_init()).

QXMutex is recursive (re-entrant), which means that it can be locked multiple times (up to 255 levels) by the same thread without causing deadlock.

QXMutex is primarily intended for the extended (blocking) threads, but can also be used by the basic threads through the non-blocking QXMutex_tryLock() API.

Note
QXMutex should be used in situations when at least one of the extended threads contending for the mutex blocks while holding the mutex (between the QXMutex_lock() and QXMutex_unlock() operations). If no blocking is needed while holding the mutex, the more efficient non-blocking mechanism of selective QXK scheduler locking should be used instead. Selective scheduler locking is available for both basic threads and extended threads, so it is applicable to situations where resources are shared among all these threads.
Usage
The following example illustrates how to instantiate and use the mutex to protect a shared resource (random seed of a pseudo-random number generator).
QXMutex l_rndMutex; // mutex to protect the random number generator
. . .
void BSP_randomSeed(uint32_t seed) {
QXMutex_init(&l_rndMutex, N_PHILO); // <=== initialize the mutex
l_rnd = seed;
}
. . .
uint32_t BSP_random(void) { // a pseudo-random-number generator
uint32_t rnd;
QXMutex_lock(&l_rndMutex); // <=== lock the shared random seed
rnd = l_rnd * (3U*7U*11U*13U*23U);
l_rnd = rnd; // set for the next time
QXMutex_unlock(&l_rndMutex); // <=== unlock the shared random seed
return rnd;
}
Blocking Mutex of the QXK preemptive kernel.
Definition qxk.h:243
void QXMutex_init(QXMutex *const me, QPrioSpec const prioSpec)
bool QXMutex_lock(QXMutex *const me, QTimeEvtCtr const nTicks)
Definition qxk_mutex.c:95
void QXMutex_unlock(QXMutex *const me)
Definition qxk_mutex.c:348

Definition at line 243 of file qxk.h.

Member Function Documentation

◆ QXMutex_init()

void QXMutex_init ( QXMutex *const me,
QPrioSpec const prioSpec )

Initialize the QXK priority-ceiling mutex QXMutex

Description
Initialize the QXK priority ceiling mutex.
Parameters
[in,out]mecurrent instance pointer (see oop)
[in]prioSpecthe priority specification for the mutex (See also QPrioSpec). This value might also be zero.
Precondition qxk_mutex:100
  • preemption-threshold must not be used
Note
prioSpec == 0 means that the priority-ceiling protocol shall not be used by this mutex. Such mutex will not change (boost) the priority of the holding threads.

Conversely, prioSpec != 0 means that the priority-ceiling protocol shall be used by this mutex. Such mutex will temporarily boost the priority and priority-threshold of the holding thread to the priority specification in prioSpec (see QPrioSpec).

Usage
The following example illustrates how to instantiate and use the mutex to protect a shared resource (random seed of a pseudo-random number generator).
QXMutex l_rndMutex; // mutex to protect the random number generator
. . .
void BSP_randomSeed(uint32_t seed) {
QXMutex_init(&l_rndMutex, N_PHILO); // <=== initialize the mutex
l_rnd = seed;
}
. . .
uint32_t BSP_random(void) { // a pseudo-random-number generator
uint32_t rnd;
QXMutex_lock(&l_rndMutex); // <=== lock the shared random seed
rnd = l_rnd * (3U*7U*11U*13U*23U);
l_rnd = rnd; // set for the next time
QXMutex_unlock(&l_rndMutex); // <=== unlock the shared random seed
return rnd;
}

◆ QXMutex_lock()

bool QXMutex_lock ( QXMutex *const me,
QTimeEvtCtr const nTicks )

Lock the QXK priority-ceiling mutex QXMutex

Parameters
[in,out]mecurrent instance pointer (see oop)
[in]nTicksnumber of clock ticks (at the associated rate) to wait for the mutex. The value of QXTHREAD_NO_TIMEOUT indicates that no timeout will occur and the mutex could block indefinitely.
Returns
'true' if the mutex has been acquired and 'false' if a timeout occurred.
Precondition qxk_mutex:200
  • this operation must NOT be called from an ISR;
  • this operation must be called from an EXTENDED thread;
  • the configured mutex-priority must be in range;
  • the calling thread must NOT be already blocked on any object.
Precondition qxk_mutex:201
  • the calling thread must NOT be holding a scheduler lock
Precondition qxk_mutex:202
  • the newly locked mutex must have no holder yet
Note
The mutex locks are allowed to nest, meaning that the same extended thread can lock the same mutex multiple times (< 255). However, each call to QXMutex_lock() must be balanced by the matching call to QXMutex_unlock().
Usage
The following example illustrates how to instantiate and use the mutex to protect a shared resource (random seed of a pseudo-random number generator).
QXMutex l_rndMutex; // mutex to protect the random number generator
. . .
void BSP_randomSeed(uint32_t seed) {
QXMutex_init(&l_rndMutex, N_PHILO); // <=== initialize the mutex
l_rnd = seed;
}
. . .
uint32_t BSP_random(void) { // a pseudo-random-number generator
uint32_t rnd;
QXMutex_lock(&l_rndMutex); // <=== lock the shared random seed
rnd = l_rnd * (3U*7U*11U*13U*23U);
l_rnd = rnd; // set for the next time
QXMutex_unlock(&l_rndMutex); // <=== unlock the shared random seed
return rnd;
}

Definition at line 95 of file qxk_mutex.c.

◆ QXMutex_tryLock()

bool QXMutex_tryLock ( QXMutex *const me)

Try to lock the QXK priority-ceiling mutex QXMutex

Parameters
[in,out]mecurrent instance pointer (see oop)
Returns
'true' if the mutex was successfully locked and 'false' if the mutex was unavailable and was NOT locked.
Precondition qxk_mutex:300
  • must NOT be called from an ISR;
  • the calling thread must be valid;
  • the mutex-priority must be in range
Precondition qxk_mutex:301
  • the thread must NOT be holding a scheduler lock.
Precondition qxk_mutex:302
  • the newly locked mutex must have no holder yet
Note
This function can be called from both basic threads (active objects) and extended threads.
The mutex locks are allowed to nest, meaning that the same extended thread can lock the same mutex multiple times (<= 255). However, each successful call to QXMutex_tryLock() must be balanced by the matching call to QXMutex_unlock().

Definition at line 244 of file qxk_mutex.c.

◆ QXMutex_unlock()

void QXMutex_unlock ( QXMutex *const me)

Unlock the QXK priority-ceiling mutex QXMutex

Parameters
[in,out]mecurrent instance pointer (see oop)
Precondition qxk_mutex:400
  • this mutex operation must NOT be called from an ISR;
  • the calling (current) thread must be EXTENDED and valid;
Precondition qxk_mutex:401
  • the mutex must be already locked at least once.
Precondition qxk_mutex:402
  • the mutex must be held by this thread.
Note
This function can be called from both basic threads (active objects) and extended threads.
The mutex locks are allowed to nest, meaning that the same extended thread can lock the same mutex multiple times (<= 225). However, each call to QXMutex_lock() or a successful call to QXMutex_tryLock() must be balanced by the matching call to QXMutex_unlock().
Usage
The following example illustrates how to instantiate and use the mutex to protect a shared resource (random seed of a pseudo-random number generator).
QXMutex l_rndMutex; // mutex to protect the random number generator
. . .
void BSP_randomSeed(uint32_t seed) {
QXMutex_init(&l_rndMutex, N_PHILO); // <=== initialize the mutex
l_rnd = seed;
}
. . .
uint32_t BSP_random(void) { // a pseudo-random-number generator
uint32_t rnd;
QXMutex_lock(&l_rndMutex); // <=== lock the shared random seed
rnd = l_rnd * (3U*7U*11U*13U*23U);
l_rnd = rnd; // set for the next time
QXMutex_unlock(&l_rndMutex); // <=== unlock the shared random seed
return rnd;
}

Definition at line 348 of file qxk_mutex.c.

Member Data Documentation

◆ ao

QActive ao
private

Active object used as a placeholder AO for this mutex in QActive_registry_[]

Definition at line 247 of file qxk.h.

◆ waitSet

QPSet waitSet
private

Set of extended-threads waiting on this mutex

Definition at line 250 of file qxk.h.


The documentation for this class was generated from the following files: