In a sequential program, work can be divided between routines within a program where one task finishes then another task can perform work. With other programs, work is executed as mini-programs within the main program where the mini-programs execute concurrently with the main program. These mini-programs can be executed as processes or threads. With processes, each process has its own address space and requires interprocess communication if the processes are to communicate. Threads sharing the address space of the process do not require special communication techniques between threads of the same process. Synchronization mechanisms such as mutexes are needed to protect share memory in order to control race conditions.
There are several models that can be used to delegate work among threads and manage when threads are created and canceled. In the delegation model, a single thread (boss) creates the threads (workers) and assigns each a task. The boss thread waits until each worker thread completes its task. With the peer-to-peer model, there is a single thread that initially creates all the threads needed to perform all the tasks; that thread is considered a worker thread and does no delegation. All threads have equal status. The pipeline model is characterized as an assembly line in which a stream of items are processed in stages. At each stage, a thread executes work performed on the unit of input. The input moves from one thread to the next, processing it until completion. The last stage or thread produces the result of the pipeline. In the producerconsumer model, there is a producer thread that produces data to be consumed by the consumer thread. The data is stored in a block of memory shared between the producer and consumer threads. Objects can be made to be multithreaded. The threads are declared within the object. A member function can create a thread that executes a free-floating function that in turn invokes one of the member functions of the object.
The Pthread library can be used to create and manage the threads of a multithreaded application. The Pthread library is based on a standardized programming interface for the creation and maintenance of threads. The thread interface has been specified by the IEEE standards committee in the POSIX 1003.1c standard. Third-party vendors supply an implementation that adheres to the POSIX standard.