Optimizations and Programming Tips

To create optimized and efficient programs, note the following:

• Always add code to your application that checks whether the application is running under the single-threaded or multi-threaded run-time system.
• Use the NOREENTRANT and NOSERIAL Compiler directives (the default) wherever possible. This minimizes stack space and call entry overhead but it is up to the programmer to ensure that a program that uses these directives is only active in one thread at a time.
• The use of the REENTRANT(1) Compiler directive increases stack space usage but does not significantly affect the call speed of the program.
• The use of the SERIAL program attribute significantly affects the speed of calls but does not affect the stack space requirements of the program.
• Use the Local-Storage Section to hold thread work variables. While this increases stack space requirements, the allocation of data is very fast.
• Using the Thread-Local-Storage Section significantly effects call speed. Replacing the Working-Storage Section with the Thread-Local-Storage Section is an easy way to make some applications to be made entirely thread-safe.

• Use mutexes for simple locking. These are the fastest of the synchronization structures.
• Use monitors to provide maximum multi-threading in programs that might cause readers and writers based problems.
• If possible, initialize all synchronization data items while in single-threaded execution. If this is not possible, then use a first time flag which is checked once before a CBL_THREAD_PROG_LOCK and checked again after obtaining the lock.
• Remember the difference between a thread and a thread handle. Create a non-detached thread only if necessary.
• Use CBL_THREAD_KILL only if absolutely necessary and if you do use it, terminate the run-unit as soon as possible afterwards. Where possible, use termination polling instead.
• Use CBL_THREAD_SUSPEND in preference to CBL_THREAD_YIELD. Avoid busy waits.
• Keep the amount of work done between CBL_THREAD_LIST_START and CBL_THREAD_LIST_END calls to a minimum.
• In certain circumstances, the application can conserve per thread memory by using the CBL_TSTORE_n routines in preference to the Thread-Local-Storage Section.
• Try to avoid deadlock rather than attempting to correct it once it has occurred.
• Avoid nesting read locks on monitors and, if you must, then be aware of the possibility of single thread deadlock.

The Compiler directives available for multi-threaded applications can affect the performance of your multi-threaded and single-threaded applications.