Richard Thompson / MutexLocker

Mutex Locker utility class to lock/unlock mbed RTOS mutexes. Create and pass a mutex, it locks the mutex then unlocks it when destroyed.

Dependents:   SmartLight HelloThreadsYo

Mutex Locker

This utility class is most useful when you have an activity that needs to be protected by a mutex that has multiple return points.

You would normally do this:

Using standard mutex access

Mutex myMutex;

void do_some_stuff()
{
  myMutex.lock();
  /* Do Stuff */

  if (condition) {
    myMutex.unlock();
    return 0;
  }

  /* Call other method */
  int temp = other_method();  // Temp so can unlock after function returns

  myMutex.unlock();
  return temp;
}

However, it's very easy to miss one of the unlock points which would later freeze the application.

Debugging this kind of error can be very hard.

The same example using MutexLocker:

Using a MutexLocker

Mutex myMutex;

int do_some_stuff()
{
  MutexLocker locker(myMutex);
  /* Do Stuff */

  if (condition) {
    return 0;
  }
  /* Call other method */
  return other_method();
  /* Mutex unlocks itself here */
}

No matter where or how your method returns, the mutex will always be unlocked as the MutexLocker goes out of scope.

mutexlocker.h@1:1a8b1de53954, 2014-04-10 (annotated)

Committer:
Tomo2k
Date:
Thu Apr 10 22:06:40 2014 +0000
Revision:
1:1a8b1de53954
Parent:
0:0714ae633eab
Child:
2:8bf85ca6ccee
Lighter weight

Who changed what in which revision?

UserRevisionLine numberNew contents of line
Tomo2k 0:0714ae633eab 1 #pragma once
Tomo2k 0:0714ae633eab 2
Tomo2k 0:0714ae633eab 3 #include "rtos.h"
Tomo2k 0:0714ae633eab 4
Tomo2k 1:1a8b1de53954 5
Tomo2k 1:1a8b1de53954 6 //! Lock/Unlokc Mutex using variable scope.
Tomo2k 1:1a8b1de53954 7 //! Ensures always unlocked regardless of method exit
Tomo2k 0:0714ae633eab 8 class MutexLocker
Tomo2k 0:0714ae633eab 9 {
Tomo2k 0:0714ae633eab 10 public:
Tomo2k 1:1a8b1de53954 11 //! Lock the mutex
Tomo2k 0:0714ae633eab 12 MutexLocker(Mutex &mutex) :
Tomo2k 1:1a8b1de53954 13 m_mutex(mutex) {
Tomo2k 1:1a8b1de53954 14 m_mutex.lock();
Tomo2k 0:0714ae633eab 15 }
Tomo2k 1:1a8b1de53954 16 //! Unlocks on destruction
Tomo2k 0:0714ae633eab 17 ~MutexLocker() {
Tomo2k 1:1a8b1de53954 18 m_mutex.unlock();
Tomo2k 0:0714ae633eab 19 }
Tomo2k 0:0714ae633eab 20 private:
Tomo2k 1:1a8b1de53954 21 Mutex &m_mutex;
Tomo2k 0:0714ae633eab 22 };