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15.1 The three multithreading APIs

Three multithreading APIs are available to Gnulib users:

• POSIX multithreading,
• ISO C multithreading,
• Gnulib multithreading.

They are supported on all platforms that have multithreading in one form or the other. Currently, these are all platforms supported by Gnulib, except for Minix.

The main differences are:

• The exit code of a thread is a pointer in the POSIX and Gnulib APIs, but only an int in the ISO C API.
• The POSIX API has additional facilities for detaching threads, setting the priority of a thread, assigning a thread to a certain set of processors, and much more.
• In the POSIX and ISO C APIs, most functions have a return code, and you are supposed to check the return code; even locking and unlocking a lock can fail. In the Gnulib API, many functions don’t have a return code; if they cannot complete, the program aborts. This sounds harsh, but such aborts have not been reported in 12 years.
• In the ISO C API, the initialization of a statically allocated lock is clumsy: You have to initialize it through a once-only function.