Bug and patch - Heavy device io can hang

[Craig White]

I'm not sure if this library is being maintained or not, but I found it was
quite useful to get some boards going with a pi!

 

I ran into a hang situation with heavy writes to an I2C device, and traced
the issue to improper mutex/condition code in dio_common.cpp.

It was very reproducible and evident that the waitForCondition method could
miss the signal from generateSignal() and just get stuck there waiting.

 

Craig

 

Here's a patch to fix the issue:

 

 

@@ -279,4 +279,10 @@

         if (sig != NULL) {

             javautil_list_add(signals, sig);

+            // Need to lock the mutex associated with the condition

+            // otherwise we could miss the signal

+            // This is done while holding the 'master' signalMutex

+
javacall_os_mutex_lock(javacall_os_cond_get_mutex(sig->condition));

+

+            // Now release the master lock

             javacall_os_mutex_unlock(signalMutex);

@@ -282,2 +288,4 @@

             javacall_os_mutex_unlock(signalMutex);

+

+            // Wait on the condition (releases the condition mutex while
waiting)

             javacall_os_cond_wait(sig->condition, timeout);

@@ -283,4 +291,9 @@

             javacall_os_cond_wait(sig->condition, timeout);

+            // Technically, this should be in a loop for spurious wakes,
but

+            // I'm not familiar enough with the code for what the loop
would check

+

+            // Unlock the condition mutex

+
javacall_os_mutex_unlock(javacall_os_cond_get_mutex(sig->condition));

         }

     } else {

         javacall_os_mutex_unlock(signalMutex);

@@ -313,4 +326,9 @@

     signal* sig = findTarget(signalType, signalTarget);

     if (sig != NULL) {

         sig->parameter = signalParameter;

+        

+        // Need to lock the mutex associated with the condition

+        // or waitForSignal could miss the signal

+        javacall_os_mutex_lock( javacall_os_cond_get_mutex(sig->condition)
);

+

         javacall_os_cond_signal(sig->condition);

@@ -316,4 +334,6 @@

         javacall_os_cond_signal(sig->condition);

+        

+        javacall_os_mutex_unlock(
javacall_os_cond_get_mutex(sig->condition) );

     } else {

         // signal is being sent before wait started

         // create the signal and add it to the list