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Upgrading a lock from read-mode to write-mode is prone to deadlocks, since whenever two threads holding reader locks both attempt to upgrade to writer locks, a deadlock is created that can only be broken by one of the threads releasing its reader lock. The deadlock can be avoided by allowing only one thread to acquire the lock in "read-mode ...
In software engineering, double-checked locking (also known as "double-checked locking optimization" [1]) is a software design pattern used to reduce the overhead of acquiring a lock by testing the locking criterion (the "lock hint") before acquiring the lock. Locking occurs only if the locking criterion check indicates that locking is required.
Contention: some threads/processes have to wait until a lock (or a whole set of locks) is released. If one of the threads holding a lock dies, stalls, blocks, or enters an infinite loop, other threads waiting for the lock may wait indefinitely until the computer is power cycled.
Sending cache is changed in S and the requesting cache is set R/F (in read miss the "ownership" is always taken by the last requesting cache) – shared intervention. – In all the other cases the data is supplied by the memory and the requesting cache is set S (V). Data stored in MM and only in one cache in E (R) state.
A cache has two primary figures of merit: latency and hit ratio. A number of secondary factors also affect cache performance. [1] The hit ratio of a cache describes how often a searched-for item is found. More efficient replacement policies track more usage information to improve the hit rate for a given cache size.
not hold the lock across system or function calls where the entity is no longer running on the processor – this can lead to deadlock; ensure that if the entity is unexpectedly exited for any reason, the lock is freed. Non-holders of the lock (a.k.a. waiters) can be held in a list that is serviced in a round-robin fashion, or in a FIFO queue ...
In computer science and software engineering, busy-waiting, busy-looping or spinning is a technique in which a process repeatedly checks to see if a condition is true, such as whether keyboard input or a lock is available. Spinning can also be used to generate an arbitrary time delay, a technique that was necessary on systems that lacked a ...
All wait-free algorithms are lock-free. In particular, if one thread is suspended, then a lock-free algorithm guarantees that the remaining threads can still make progress. Hence, if two threads can contend for the same mutex lock or spinlock, then the algorithm is not lock-free. (If we suspend one thread that holds the lock, then the second ...