Состояние гонки (англ. race condition), также конкуренция — ошибка проектирования многопоточной системы или приложения, при которой работа системы или приложения зависит от того, в каком порядке выполняются части кода. Своё название ошибка получила от похожей ошибки проектирования электронных схем (см. Гонки сигналов).
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- In programming, two main types of race conditions occur in a critical section of code, which is a section of code executed by multiple threads.
- In practice, many race conditions are caused by data races, and many data races lead to race conditions, but those two problems are not dependent on each other.
- Inside computer software – one of the most prominent areas of race conditions – there are a wide variety of race conditions possible.
- Способы борьбы с race condition: Оптимистическая блокировка (Optimistic Locking): Это подход, при котором система предполагает, что конфликты...
- A dynamic race condition occurs when it results in multiple transitions when only one is intended. They are due to interaction between gates.
- Под конец могу сказать, что гораздо полезнее выявлять Race Condition, чем Data Race, Data Race даже иногда может быть полезным и приводить к...
- A race condition is a semantic error. It is a flaw that occurs in the timing or the ordering of events that leads to erroneous program behavior.
- Race Condition. Every software, system, or electronic device is based on a certain program, sequence, and algorithm.
- ...dosya indirildikten sonra, network thread'inden cağrılan callback methodu, graphics thread'inin elleştiği bir resource'a müdahale ederken race condition...
- Из-за высокой параллельности веб-приложений race condition может возникать чаще, если её не обработать должным образом.
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A race condition occurs when two or more threads can access shared data and they try to change it at the same time. Because the thread scheduling algorithm can swap between threads at any time, you don't know the order in which the threads will attempt to access the shared data. Therefore, the result of the change in data is dependent on the thread scheduling algorithm, i.e. both threads are "racing" to access/change the data. Problems often occur when one thread does a "check-then-act" (e.g. "check" if the value is X, then "act" to do something that depends on the value being X) and another thread does something to the value in between the "check" and the "act". E.g:The point being, y could be 10, or it could be anything, depending on whether another thread changed x in between the check and act. You have no real way of knowing.In order to prevent race conditions from occurring, you would typically put a lock around the shared data to ensure only one thread can access the data at a time. This would mean something like this:
if (x == 5) // The "Check"{ y = x * 2; // The "Act" // If another thread changed x in between "if (x == 5)" and "y = x * 2" above, // y will not be equal to 10.}// Obtain lock for xif (x == 5){ y = x * 2; // Now, nothing can change x until the lock is released. // Therefore y = 10}// release lock for x