Multithreading Terms

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Figure 1, Table 1, Multithreading Terms introduces some of the terms that are used in this guide.

Table 1 Multithreading Terms

Term	Definition
Process	The UNIX environment, such as file descriptors, user ID, and so on, created with the `fork(2)` system call, which is set up to run a program.
Thread	A sequence of instructions executed within the context of a process.
POSIX `pthreads`	A threads interface that is POSIX threads compliant. See Multithreading Programming in Oracle Solaris for more information.
Oracle Solaris `threads`	An Oracle Solaris threads interface that is not POSIX threads compliant. A predecessor of pthreads.
Single-threaded	Restricts access to a single thread. Execution is through sequential processing, limited to one thread of control.
Multithreading	Allows access to two or more threads. Execution occurs in more than one thread of control, using parallel or concurrent processing.
User-level or Application-level threads	Threads managed by threads routines in user space, as opposed to kernel space. The POSIX pthreads are used to create and handle user threads. In this guide, and in general, a thread is a user-level thread. Note - Because this guide is for application programmers, kernel thread programming is not discussed.
Lightweight processes	Kernel threads, also called LWPs, that execute kernel code and system calls. LWPs are managed by the system thread scheduler, and cannot be directly controlled by the application programmer. Beginning with Solaris 9, every user-level thread has a dedicated LWP. This is known as a 1:1 thread model.
Bound thread (obsolete term)	Prior to Solaris 9, a user-level thread that is permanently bound to one LWP. Beginning with Solaris 9, every thread has a dedicated LWP, so all threads are bound threads. The concept of an unbound thread no longer exists.
Unbound thread (obsolete term)	Prior to Solaris 9, a user-level thread that is not necessarily bound to one LWP. Beginning with Solaris 9, every thread has a dedicated LWP, so the concept of unbound threads no longer exists.
Attribute object	Contains opaque data types and related manipulation functions. These data types and functions standardize some of the configurable aspects of POSIX threads, mutual exclusion locks (mutexes), and condition variables.
Mutual exclusion locks	Objects used to lock and unlock access to shared data. Such objects are also known as mutexes.
Condition variables	Objects used to block threads until a change of state.
Read-write locks	Objects used to allow multiple read-only access to shared data, but exclusive access for modification of that data.
Counting semaphore	A memory-based synchronization mechanism in which a non-negative integer count is used to coordinate access by multiple threads to shared resources.
Parallelism	A condition that arises when at least two threads are executing simultaneously.
Concurrency	A condition that exists when at least two threads are making progress. A more generalized form of parallelism that can include time-slicing as a form of virtual parallelism.