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Thread safety is a computer programming concept applicable in the context of multi-threaded programs. A piece of code is thread-safe if it only manipulates shared data structures in a manner that guarantees safe execution by multiple threads at the same time. There are various strategies for making thread-safe data structures. A program may execute code in several threads simultaneously in a shared address space where each of those threads has access to virtually all of the memory of every other thread. Thread safety is a property that allows code to run in multi-threaded environments by re-establishing some of the correspondences between the actual flow of control and the text of the program, by means of synchronization. == Levels of thread safety == Software libraries can provide certain thread-safety guarantees. For example, concurrent reads might be guaranteed to be thread-safe, but concurrent writes might not be. Whether or not a program using such a library is thread-safe depends on whether it uses the library in a manner consistent with those guarantees. Different vendors use slightly different terminology for thread-safety: * Thread safe: Implementation is guaranteed to be free of race conditions when accessed by multiple threads simultaneously. * Conditionally safe: Different threads can access different objects simultaneously, and access to shared data is protected from race conditions. * Not thread safe: Code should not be accessed simultaneously by different threads. Thread safety guarantees usually also include design steps to prevent or limit the risk of different forms of deadlocks, as well as optimizations to maximize concurrent performance. However, deadlock-free guarantees can not always be given, since deadlocks can be caused by callbacks and violation of architectural layering independent of the library itself. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「thread safety」の詳細全文を読む スポンサード リンク
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