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.



• 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.