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<== Date ==> <== Thread ==>
Subject: lock/unlock mutex problem
From: "Dudley, David via Tech-talk" <tech-talk at aps.anl.gov>
To: "tech-talk at aps.anl.gov" <tech-talk at aps.anl.gov>
Date: Thu, 6 Feb 2020 14:41:30 +0000

I’ve run into a particular problem that I haven’t been able to figure out yet.

 

I’m debugging a device driver that uses a number of concurrent threads for operation

 

This is with epics 3.15.7.

 

I have these routines in my code

 

 

In my class definition, I’ve got:

char locker[80];                 // Store name of routine that called the lock/unlock

epicsMutex *mutex;      // Mutex for concurrent access control

 

The instantiation routine invokes:

this->mutex = newEpicsMutex;

 

The code in my class includes:

 

/** Lock the variable for concurrent access */

void driver::lock(const char *caller)

{

                bool flag;

                unsigned int lockedflag=0;

                do

                {

                                flag = this->mutex->tryLock();

                                if(!flag)

                                {

                                                lockedflag++;

                                                if((!(lockedflag %10) && lockedflag < 100) || (!(lockedflag %100) && lockedflag < 1000) || (!(lockedflag % 1000) && lockedflag < 10000) )

                                                                outputConsoleMessage(SHOW_ERROR_MESSAGES,"Driver::lock() - was called by %s->%s, but the variable has been locked by \"%s\" for %f secs!\n",caller, this->rec->name, locker, 0.01*lockedflag);

                                                epicsThreadSleep(0.01);

                                }

                }

                while(!flag);

                strncpy(locker,caller,sizeof(locker) );

}

 

/** Unock the variable for concurrent access */

void driver::unlock(const char *caller)

{

                this->mutex->unlock();

                strncpy(locker,"Unlocked", sizeof(locker));

}

 

There are a number of lock/unlock pairs in the code that lock/unlock access to retrieved data.

 

After some period of time, which may be as short as a few minutes, or as long as many hours, I start getting errors like this:

2020/02/05 18:44:42.6571 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.010000 secs!

2020/02/05 18:44:42.6694 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.020000 secs!

2020/02/05 18:44:42.6802 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.030000 secs!

2020/02/05 18:44:42.6911 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.040000 secs!

2020/02/05 18:44:42.7020 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.050000 secs!

2020/02/05 18:44:42.7128 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.060000 secs!

2020/02/05 18:44:42.7237 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.070000 secs!

2020/02/05 18:44:42.7345 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.080000 secs!

2020/02/05 18:44:42.7453 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.090000 secs!

2020/02/05 18:44:42.7562 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.100000 secs!

2020/02/05 18:44:42.8643 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.200000 secs!

2020/02/05 18:44:42.9725 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.300000 secs!

2020/02/05 18:44:43.0858 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.400000 secs!

2020/02/05 18:44:43.1941 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.500000 secs!

2020/02/05 18:44:43.3022 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.600000 secs!

2020/02/05 18:44:43.4105 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.700000 secs!

2020/02/05 18:44:43.5187 Driver::lock() - was called by Driver::retry->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.800000 secs!

2020/02/05 18:44:43.6072 Driver::lock() - was called by Driver::setProcessRecord->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.010000 secs!

2020/02/05 18:44:43.6181 Driver::lock() - was called by Driver::setProcessRecord->_DSC_CHW:VFC_N2000:CI_CSET_RBV, but the variable has been locked by "Unlocked" for 0.020000 secs!

2020/02/05 18:44:43.6269 Driver::lock() - was called by Driver::clear_retry_count->CT1, but the variable has been locked by "Driver::thread_main" for 0.900000 secs!

 

 

Now, this driver has been working on 3.15.2, but when updated to 3.5.7, all of a sudden I’ve got this problem.

 

I don’t see how the mutex can be locked when the routine shows it is “Unlocked”.

Please, someone see something I don’t!

 

Thanks-

 

David Dudley

Controls Engineer III

Facility for Rare Isotope Beams

Michigan State University

640 South Shaw Lane

East Lansing, MI 48824-1321, USA

Tel. 517-908-7133

Email: dudleyd@frib.msu.edu

 

 

cid:image002.jpg@01D07041.57B6D750

 

 

Replies:
Re: lock/unlock mutex problem Johnson, Andrew N. via Tech-talk
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