Bug and patch - Heavy device io can hang

[Sergey Nazarkin]

Hi, Craig!

Thanks for the fix. I’ll take a look on Monday


Sergey Nazarkin




> On 25 May 2018, at 07:57, Craig White <cwhite102 at gmail.com> wrote:
> 
> 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
> 
>