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POpthread_mutex_timedlock and the deadlock
 

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  1. POpthread_mutex_timedlock and the deadlock
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    <p>Typically if a task1 holds lock A wants to take a lock B and another task2 has taken lock B and is waiting for lock A held by task1), this causes the deadlock.</p> <p>But when it comes to pthread_mutex_timedlock, it attempts the mutex lock or timeout after the specified timeout.</p> <p>I hit the deadlock scenario where i was trying to take the timed lock, which would have timed out eventually, which puzzles me.</p> <p><strong>edit: Deadlocks can be avoided by having a better design, which is what i ended up doing, i made sure that the order of taking mutex locks is same, to avoid deadlock but the question remains open as to if the deadlock can be avoided since i chose timedlock</strong> </p> <p>Can someone explain me this behaviour ?</p> <p><strong>Edit: Attaching a sample code to make the scenario more clear(real tasks are fairly complicated and run into thousands of lines)</strong></p> <p>T1 </p> <pre><code>pthread_mutex_lock(&amp;lockA); //call some API, which results in a lock of m2 pthread_mutex_lock(&amp;lockB); //unlock in the order pthread_mutex_unlock(&amp;lockB); pthread_mutex_unlock(&amp;lockA); </code></pre> <p>T2</p> <pre><code>pthread_mutex_lock(&amp;lockB); //call some API, which results in locking m1 pthread_mutex_timedlock(&amp;lockA,&lt;10 sec&gt;); </code></pre> <p>The crash is seen in the context of T2, bt:</p> <pre><code>Program terminated with signal 6, Aborted. #0 0x57edada0 in raise () from /lib/libc.so.6 (gdb) bt #0 0x57edada0 in raise () from /lib/libc.so.6 #1 0x57edc307 in abort () from /lib/libc.so.6 #2 0x57ed4421 in __assert_fail () from /lib/libc.so.6 #3 0x57bb2a7c in pthread_mutex_timedlock () from /lib/libpthread.so.0 </code></pre> <p>I traced the error to following </p> <pre><code>pthread_mutex_timedlock: Assertion `(-(e)) != 35 || (kind != PTHREAD_MUTEX_ERRORCHECK_NP &amp;&amp; kind != PTHREAD_MUTEX_RECURSIVE_NP)' failed. </code></pre>
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    1. USHasturkun
    1. USrajshenoy
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      1. VTUpMod
    2. VO
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    1. COHard to tell without seeing any code.
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      1. USMaxim Egorushkin
    2. COI added some more information. hope that helps
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      1. USrajshenoy
    3. COMaybe I am misreading your question but it's not clear to me that you understand the timeout is how long will be *waited* to acquire the lock not how long it actually *holds* the lock. Is that the source of your problem or am I misinterpreting what you saying due to the multiple edits of the question?
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      1. USDuck
 

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