Helgrind detects a large number of errors involving the pthreads API, as summarized by its manual, and listed next:

• Unlocking an invalid mutex
• Unlocking a not-locked mutex
• Unlocking a mutex held by a different thread
• Destroying an invalid or a locked mutex
• Recursively locking a non-recursive mutex
• Deallocation of memory that contains a locked mutex
• Passing mutex arguments to functions expecting reader-writer lock arguments, and vice versa
• Failure of a POSIX pthread function fails with an error code that must be handled
• A thread exits whilst still holding locked locks
• Calling pthread_cond_wait with a not-locked mutex, an invalid mutex, or one locked by a different thread
• Inconsistent bindings between condition variables and their associated mutexes
• Invalid or duplicate initialization of a pthread barrier
• Initialization of a pthread barrier on which threads are still waiting
• Destruction of a pthread barrier object which was never initialized, or on which threads are still waiting
• Waiting on an uninitialized pthread barrier

In addition to this, if Helgrind itself does not detect an error, but the pthreads library itself returns an error for each function which Helgrind intercepts, an error is reported by Helgrind as well.