i5/OS Pthreads versus the POSIX standard, the Single UNIX Specification, and other threads implementations

Although the Pthread interfaces described in this document are based on a subset of the APIs defined in the POSIX standard and the Single UNIX Specification, the implementation of these APIs is not compliant with these standards. This means that applications written in other versions of threads are not necessarily portable to i5/OS. Below is a list of the differences between the Pthread APIs and other threads implementations.

• All thread definitions in pthread.h
• Unsupported preprocessor and feature test macros
• Unsupported APIs
• Unsupported constants
• Unsupported cancellation points
• Unsupported sysconf() configuration variables
• Thread priority and scheduling
• Thread ID vs. Pthread Handle (pthread_t)
• Thread ID value and size
• Mutexes return EDEADLK when re-locked by owner
• Return values from thread start routines are not integers
• Threads do not necessarily start before pthread_create() returns
• Initial thread is special, cannot pthread_exit()
• Pthread APIs cause asynchronous signals initialization
• Not all jobs can create threads; pthread_create() fails with EBUSY
• Read/write locks are recursive
• Shared read/write locks are released at thread termination
• Read/write locks can be upgraded / downgraded
• Read/write locks do not favor writers
• Spawn API provides more POSIX-like process model
• C++ destructors and Pthread termination
• Unhandled exceptions terminate the thread (not the process)
• Exceptions vs. Asynchronous signals vs. ANSI C signals
• Mutexes can be named to aid in application debug