### Global Lock

Use a global lock, which has the characteristics of a recursive mutex, instead of a regular mutex when calling routines that you think are nonreentrant. (When in doubt, assume the code is nonreentrant.)

The pthread_lock_global_np( ) routine is a locking protocol that is used to call nonreentrant routines, often found in existing library packages that were not designed to run in a multithreaded environment.

The way to call a library function that is not reentrant from a multithreaded program is to protect the function with a mutex. If every function that calls a library locks a particular mutex before the call and releases the mutex after the call, then the function completes without interference. However, this is difficult to do successfully because the function may be called by many libraries. A global lock solves this problem by providing a universal lock. Any code that calls any nonreentrant function uses the same lock.

To lock a global lock, call the pthread_lock_global_np( ) routine. To unlock a global lock, call the pthread_unlock_global_np( ) routine.

Note: Many COBOL and FORTRAN compilers generate inherently nonreentrant code. Many C, Ada, Pascal, and BLISS compilers generate reentrant code by default. It is possible to write nonreentrant code in the reentrant languages by not following a locking protocol.

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