Acquire-release semantics
Acquire-release semantics are memory-ordering rules under which release operations make preceding effects visible to acquire operations that synchronize with them.
C++ Concurrency in Action, Second Edition
Acquire-release ordering provides synchronization when an acquire operation reads a value written by a release operation, without imposing a single global order.
- How it is used
- Coordinates visibility of writes between threads without requiring sequential consistency.
- How deep it goes
- Works through matching release and acquire operations, their ordering of relaxed writes, transitive synchronization, and the absence of total order.
- Examples
- Uses two atomic flags, a release-published relaxed write, and a three-thread synchronization chain.
- What you can do after
- Apply it via std::atomic release stores and acquire loads to publish earlier writes between threads.
Read how C++ Concurrency in Action, Second Edition explains acquire-release semantics →
Modern C
A release operation is a concurrency operation that publishes preceding effects so that a corresponding acquire can observe them.
- How it is used
- Establishes visibility of one thread’s earlier effects to another through paired synchronization operations.
- How deep it goes
- Defines the synchronization rule and visibility consequence, then identifies atomic memory orders and library pairs without developing implementation internals.
- Examples
- Uses an input/account-thread exchange, call_once initialization, and atomic_fetch_add_explicit with memory_order_acq_rel.
- What you can do after
- Apply it via C atomic _explicit interfaces or paired library calls to make preceding effects visible across threads.
Modern C, Third Edition
Release semantics are memory-ordering properties that make preceding effects available to a thread that synchronizes with the release operation.
- How it is used
- Establishes when effects in one thread become visible to another through atomic operations or C library synchronization.
- How deep it goes
- Defines directional operations and the read-from synchronization rule, then states its visibility consequence; defers relaxed atomic operations.
- Examples
- Uses two threads exchanging an atomic value and a table of C library release-acquire pairs.
- What you can do after
- Evaluate/understand whether an atomic read or mutex acquisition makes another thread’s preceding effects visible.
Read how Modern C, Third Edition explains acquire-release semantics →
C# Concurrency: Asynchronous and multithreaded programming
Release semantics are memory-ordering guarantees that prevent writes from being moved later than a synchronization operation.
- How it is used
- Protects visibility of shared-data updates when a thread releases a lock.
- How deep it goes
- Defines write-ordering guarantees and relates them to locks, acquire operations, memory barriers, and the memory model.
- Examples
- Uses lock release and Figure 7.1 to illustrate writes becoming available to the next thread.
- What you can do after
- Apply it by locking shared-data access so released changes become visible to the next thread.
Related concepts
- acquire semanticsconfigured by · Acquire semantics prevent subsequent memory operations from being reordered before an acquire operation and make visible effects that happen-before it, including those published by a synchronizing release operation.
- std::memory_order_releaseconfigured by · A C++ memory-order value that gives an atomic store release semantics, making preceding operations visible to a thread that performs a matching acquire operation.
- sequential consistencycontrasts with · Sequential consistency is a memory model in which participating operations appear in a single total order that preserves each thread’s program order.
- read-modify-write operationused by · An operation that reads a value from a location, computes or selects an update, and writes the resulting value back to that location.
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