Glossary

• application  

  A specific style of program that displays a graphical interface to the user.



• condition  

  A construct used to synchronize access to a resource. A thread waiting on a condition is not allowed to proceed until another thread explicitly signals the condition.



• critical section  

  A portion of code that must be executed by only one thread at a time.



• input source  

  A source of asynchronous events for a thread. Input sources can be port-based or manually triggered and must be attached to the thread’s run loop.



• joinable thread  

  A thread whose resources are not reclaimed immediately upon termination. Joinable threads must be explicitly detached or be joined by another thread before the resources can be reclaimed. Joinable threads provide a return value to the thread that joins with them.



• main thread  

  A special type of thread created when its owning process is created. When the main thread of a program exits, the process ends.



• mutex  

  A lock that provides mutually exclusive access to a shared resource. A mutex lock can be held by only one thread at a time. Attempting to acquire a mutex held by a different thread puts the current thread to sleep until the lock is finally acquired.



• operation object  

  An instance of the NSOperation class. Operation objects wrap the code and data associated with a task into an executable unit.



• operation queue  

  An instance of the NSOperationQueue class. Operation queues manage the execution of operation objects.



• process  

  The runtime instance of an application or program. A process has its own virtual memory space and system resources (including port rights) that are independent of those assigned to other programs. A process always contains at least one thread (the main thread) and may contain any number of additional threads.



• program  

  A combination of code and resources that can be run to perform some task. Programs need not have a graphical user interface, although graphical applications are also considered programs.



• recursive lock  

  A lock that can be locked multiple times by the same thread.



• run loop  

  An event-processing loop, during which events are received and dispatched to appropriate handlers.



• run loop mode  

  A collection of input sources, timer sources, and run loop observers associated with a particular name. When run in a specific “mode,” a run loop monitors only the sources and observers associated with that mode.



• run loop object  

  An instance of the NSRunLoop class or CFRunLoopRef opaque type. These objects provide the interface for implementing an event-processing loop in a thread.



• run loop observer  

  A recipient of notifications during different phases of a run loop’s execution.



• semaphore  

  A protected variable that restricts access to a shared resource. Mutexes and conditions are both different types of semaphore.



• task  

  A quantity of work to be performed. Although some technologies (most notably Carbon Multiprocessing Services) use this term differently, the preferred usage is as an abstract concept indicating some quantity of work to be performed.



• thread  

  A flow of execution in a process. Each thread has its own stack space but otherwise shares memory with other threads in the same process.



• timer source  

  A source of synchronous events for a thread. Timers generate one-shot or repeated events at a scheduled future time.