Oracle® Solaris Studio 12.4: Thread Analyzer User's Guide

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Updated: December 2014

What is a Deadlock?

Deadlock describes a condition in which two or more threads are blocked forever because they are waiting for each other. There are many causes of deadlocks. Thread Analyzer detects deadlocks that are caused by the inappropriate use of mutual exclusion locks. This type of deadlock is commonly encountered in multithreaded applications.

    A process with two or more threads can deadlock when all of the following conditions are true:

  • Threads that are already holding locks request new locks

  • The requests for new locks are made concurrently

  • Two or more threads form a circular chain in which each thread waits for a lock which is held by the next thread in the chain

    Here is a simple example of a deadlock condition:

  • Thread 1 holds lock A and requests lock B

  • Thread 2 holds lock B and requests lock A

A deadlock can be of two types: A potential deadlock or an actual deadlock. A potential deadlock does not necessarily occur in a given run, but can occur in any execution of the program depending on the scheduling of threads and the timing of lock requests by the threads. An actual deadlock is one that occurs during the execution of the program. An actual deadlock causes the threads involved to hang, but might cause the whole process to hang.