A path of execution through a program in memory. With traditional systems, each process on the system has only one thread of execution. On a multithreaded system, several threads can be started within one process. Threads within a process share the same access to the process resources such as memory and open file descriptors.
Multithreaded systems typically provide the following features:
Thread-management routines to create and destroy threads.
A thread scheduler that manages the simultaneous execution of multiple threads within the same process.
Thread serialization primitives for ensuring that access to shared resources from different threads is mutually exclusive. That is, if one thread has begun to access a shared resource, then no other thread must access the resource until the first one is finished. For example, if a linked list is shared by multiple threads, then each traversal, insertion, and deletion operation is a critical section that must be serialized with other traversals, insertions, or deletions. All such critical sections must be serialized so that the execution a critical section in one thread is not interleaved with the execution of a related critical section in another thread. A serialization primitive consists of a lockable object (for instance, a mutex) and routines to lock and unlock the object.
Thread synchronization primitives for synchronizing dependent actions performed by different threads. A synchronization primitive consists of a synchronization object (for instance, a condition variable), a routine to wait on the condition, and a routine to signal that the condition is satisfied.
