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

Committer:
Tomo2k
Date:
2014-04-10
Revision:
3:aab6944f2ed3
Parent:
2:8bf85ca6ccee

File content as of revision 3:aab6944f2ed3:

/* (C) 2014 Richard Thompson (Tomo2k)
This software is Apache 2.0 licenced for this to be reused.

That said, it's trivial and rather obvious!
*/
#pragma once

#include "rtos.h"


//! Lock/Unlock Mutex using variable scope.
//! Ensures always unlocked regardless of method exit
class MutexLocker
{
public:
    //! Lock the mutex
    MutexLocker(Mutex &mutex) :
        m_mutex(mutex) {
        m_mutex.lock();
    }
    //! Unlocks on destruction
    ~MutexLocker() {
        m_mutex.unlock();
    }
private:
    Mutex &m_mutex;
    // Disable copy
    MutexLocker & operator=(const MutexLocker&);
    MutexLocker(const MutexLocker &);
};