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However, deadlock-free guarantees cannot always be given, since deadlocks can be caused by callbacks and violation of architectural layering independent of the library itself. Software libraries can provide certain thread-safety guarantees. [5] For example, concurrent reads might be guaranteed to be thread-safe, but concurrent writes might not be.
m.lock() — mutex locked; callback(1) lock_and_call(0) — because i > 0; m.lock() — deadlock, because m is already locked, so the executing thread will block, waiting for itself. Replacing the mutex with a recursive one solves the problem, because the final m.lock() will succeed without blocking.
Two warded lock keys and a homemade skeleton key. A skeleton key (also known as a passkey [1]) is a type of master key in which the serrated edge has been removed in such a way that it can open numerous locks, [2] most commonly the warded lock. The term derives from the fact that the key has been reduced to its essential parts. [2]
Generally, locks are advisory locks, where each thread cooperates by acquiring the lock before accessing the corresponding data. Some systems also implement mandatory locks, where attempting unauthorized access to a locked resource will force an exception in the entity attempting to make the access. The simplest type of lock is a binary ...
A few multi-core processors have a "power-conscious spin-lock" instruction that puts a processor to sleep, then wakes it up on the next cycle after the lock is freed. A spin-lock using such instructions is more efficient and uses less energy than spin locks with or without a back-off loop. [6]
A wait-for graph in computer science is a directed graph used for deadlock detection in operating systems and relational database systems.. In computer science, a system that allows concurrent operation of multiple processes and locking of resources and which does not provide mechanisms to avoid or prevent deadlock must support a mechanism to detect deadlocks and an algorithm for recovering ...
A lock convoy occurs when multiple threads of equal priority contend repeatedly for the same lock. [1] [2] Unlike deadlock and livelock situations, the threads in a lock convoy do progress; however, each time a thread attempts to acquire the lock and fails, it relinquishes the remainder of its scheduling quantum and forces a context switch. The ...
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 ...