QP::QXMutex Class Reference

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

#include "qxk.hpp"

Public Member Functions
	QXMutex ()
void	init (QPrioSpec const prioSpec) noexcept
bool	lock (QTimeEvtCtr const nTicks=QXTHREAD_NO_TIMEOUT) noexcept
bool	tryLock () noexcept
void	unlock () noexcept

Private Attributes
QActive	m_ao
QPSet	m_waitSet

Detailed Description

Blocking Mutex of the QXK preemptive kernel.

Details

QP::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, QP::QXMutex requires its own unique QP priority level, which cannot be used by any thread or any other QP::QXMutex.

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

QP::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.

QP::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

QP::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).

QP::QXMutex TH_mutex;  // <===
. . .
void XThread2::run(QP::QXThread * const thr) {
    TH_mutex.init(APP::N_PHILO + 6U); // priority-ceiling mutex
 
    for (;;) {
        . . .
        TH_mutex.lock(QP::QXTHREAD_NO_TIMEOUT); // lock the mutex
        QP::QXThread::delay(5U);  // wait more (BLOCK)
        TH_mutex.unlock();
    }
}

Definition at line 164 of file qxk.hpp.

Constructor & Destructor Documentation

QXMutex()

QP::QXMutex::QXMutex

(

)

Definition at line 76 of file qxk_mutex.cpp.

Member Function Documentation

init()

void QP::QXMutex::init ( QPrioSpec const prioSpec )

noexcept

Initialize the QXK priority-ceiling mutex QP::QXMutex

Details

Initialize the QXK priority ceiling mutex.

Parameters

[in]

prioSpec

the priority specification for the mutex (See also QP::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 QP::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).

QP::QXMutex TH_mutex;
. . .
void XThread2::run(QP::QXThread * const thr) {
    TH_mutex.init(APP::N_PHILO + 6U);  // <===
 
    for (;;) {
        . . .
        TH_mutex.lock(QP::QXTHREAD_NO_TIMEOUT); // lock the mutex
        QP::QXThread::delay(5U);  // wait more (BLOCK)
        TH_mutex.unlock();
    }
}

Definition at line 81 of file qxk_mutex.cpp.

lock()

bool QP::QXMutex::lock ( QTimeEvtCtr const nTicks = QXTHREAD_NO_TIMEOUT )

noexcept

Lock the QXK priority-ceiling mutex QXMutex

Parameters

[in]

nTicks

number of clock ticks (at the associated rate) to wait for the mutex. The value of QP::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).

QP::QXMutex TH_mutex;
. . .
void XThread2::run(QP::QXThread * const thr) {
    TH_mutex.init(APP::N_PHILO + 6U);
 
    for (;;) {
        . . .
        TH_mutex.lock(QP::QXTHREAD_NO_TIMEOUT); // <===
        QP::QXThread::delay(5U);  // wait more (BLOCK)
        TH_mutex.unlock();
    }
}

Definition at line 99 of file qxk_mutex.cpp.

tryLock()

bool QP::QXMutex::tryLock ( )

noexcept

Try to lock the QXK priority-ceiling mutex QP::QXMutex

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 246 of file qxk_mutex.cpp.

unlock()

void QP::QXMutex::unlock ( )

noexcept

Unlock the QXK priority-ceiling mutex QP::QXMutex

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).

QP::QXMutex TH_mutex;
. . .
void XThread2::run(QP::QXThread * const thr) {
    TH_mutex.init(APP::N_PHILO + 6U);
 
    for (;;) {
        . . .
        TH_mutex.lock(QP::QXTHREAD_NO_TIMEOUT);
        QP::QXThread::delay(5U);  // wait more (BLOCK)
        TH_mutex.unlock(); // <===
    }
}

Definition at line 350 of file qxk_mutex.cpp.

Member Data Documentation

m_ao

QActive QP::QXMutex::m_ao

private

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

Definition at line 166 of file qxk.hpp.

m_waitSet

QPSet QP::QXMutex::m_waitSet

private

Set of extended-threads waiting on this mutex

Definition at line 167 of file qxk.hpp.

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

• qxk.hpp
• qxk_mutex.cpp
• qxk.dox