When a thread object goes out of scope and it is in joinable state, the program is terminated. The Standard Committee had two other options for the destructor of a joinable thread. It could quietly join — but join might never return if the thread is stuck. Or it could detach the thread (a detached … Read more
a Control that was constructed off the UI thread… Yes, that is a good way to trigger this problem. The underlying problem is caused by the SystemEvents class, it has the unenviable task of raising its events on the correct thread. The UserPreferenceChanged event is the typical trouble-maker, lots of controls subscribe it so they … Read more
You can do this programmatically using the ThreadMXBean that ships with the JDK: ThreadMXBean bean = ManagementFactory.getThreadMXBean(); long[] threadIds = bean.findDeadlockedThreads(); // Returns null if no threads are deadlocked. if (threadIds != null) { ThreadInfo[] infos = bean.getThreadInfo(threadIds); for (ThreadInfo info : infos) { StackTraceElement[] stack = info.getStackTrace(); // Log or store stack trace information. … Read more
You can use pthread_mutex_trylock. If that succeeds, the mutex was unclaimed and you now own it (so you should release it and return “unheld”, in your case). Otherwise, someone is holding it. I have to stress though that “check to see if a mutex is unclaimed” is a very bad idea. There are inherent race … Read more
You’re not just starting another thread – you’re joining on it. That new thread has to wait for StaticInitializer to be fully initialized before it can proceed, because it’s trying to set the state field… and initialization is already in progress, so it waits. However, it’s going to be waiting forever, because that initialization is … Read more
According to MSDN: http://msdn.microsoft.com/en-us/library/ms191242.aspx When either the READ COMMITTED SNAPSHOT or ALLOW SNAPSHOT ISOLATION database options are ON, logical copies (versions) are maintained for all data modifications performed in the database. Every time a row is modified by a specific transaction, the instance of the Database Engine stores a version of the previously committed image … Read more
Since JDK 1.5 there are very useful methods in the java.lang.management package to find and inspect deadlocks that occurs. See the findMonitorDeadlockedThreads() and findDeadlockedThreads() method of the ThreadMXBean class. A possible way to use this is to have a separate watchdog thread (or periodic task) that does this. Sample code: ThreadMXBean tmx = ManagementFactory.getThreadMXBean(); long[] … Read more
UPDATE: This question was the subject of my blog in January 2013. Thanks for the great question! How can we write a program that will always go into deadlock no matter how the threads are scheduled? Here’s an example in C#. Note that the program appears to contain no locks and no shared data. It … Read more
In the simple case given, unlocking in the reverse order is not necessary to avoid a deadlock. However, as the code gets more complicated, unlocking in the reverse order helps you maintain proper lock ordering. Consider: A.lock(); B.lock(); Foo(); A.unlock(); Bar(); B.unlock(); If Bar() attempts to reacquire A, you’ve effectively broken your lock ordering. You’re … Read more
A lock occurs when multiple processes try to access the same resource at the same time. One process loses out and must wait for the other to finish. A deadlock occurs when the waiting process is still holding on to another resource that the first needs before it can finish. So, an example: Resource A … Read more