Editing Thread (computing) (section)

===Threads and data synchronization===
{{anchor|Synchronization}}
{{Main|Thread safety}}
Threads in the same process share the same address space. This allows concurrently running code to [[coupling (computer science)|couple]] tightly and conveniently exchange data without the overhead or complexity of an [[inter-process communication|IPC]]. When shared between threads, however, even simple data structures become prone to [[Race condition#Computing|race conditions]] if they require more than one CPU instruction to update: two threads may end up attempting to update the data structure at the same time and find it unexpectedly changing underfoot. Bugs caused by race conditions can be very difficult to reproduce and isolate.

To prevent this, threading [[application programming interface]]s (APIs) offer [[synchronization primitive]]s such as [[mutex]]es to [[Lock (computer science)|lock]] data structures against concurrent access. On uniprocessor systems, a thread running into a locked mutex must sleep and hence trigger a context switch. On multi-processor systems, the thread may instead poll the mutex in a [[spinlock]]. Both of these may sap performance and force processors in [[symmetric multiprocessing]] (SMP) systems to contend for the memory bus, especially if the [[Lock (computer science)#Granularity|granularity]] of the locking is too fine.

Other synchronization APIs include [[condition variables]], [[critical section]]s, [[Semaphore (programming)|semaphores]], and [[Monitor (synchronization)|monitors]].