Acquire-release semantics

As explained in C# Concurrency: Asynchronous and multithreaded programming

Release semantics are memory-ordering guarantees that prevent writes from being moved later than a synchronization operation.

Release semantics prevent writes from moving later than a synchronization operation. Releasing a lock writes shared changes back to memory, making them available to the next thread that acquires it. section 7.2

Use release semantics as part of a broader memory-ordering discipline:

• Pair lock release with acquire semantics: acquisition prevents reads from moving earlier, while release prevents writes from moving later. section 7.2
• Protect shared data with locks rather than relying on C# volatile semantics, which may not guarantee the latest value. section 7.2
• Treat memory barriers and the memory model as the mechanisms governing which compiler and CPU reorderings remain allowed. section 7.2

Figure 7.1 Acquire and release semantics

Figure 7.1 visualizes how acquire and release semantics constrain memory-operation movement. section 7.2

How C# Concurrency: Asynchronous and multithreaded programming covers it

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 it assumes

Introduces acquire semantics, release semantics, memory barriers, and the memory model while discussing shared-data access.

What you can do after

Apply it by locking shared-data access so released changes become visible to the next thread.

How it connects

Connects lock release with acquire semantics, memory barriers, the memory model, and shared data.

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Also explained in

• 

  liveBookmanning.com
  C++ Concurrency in Action, Second EditionAcquire-release ordering provides synchronization when an acquire operation reads a value written by a release operation, without imposing a single global order.
• 

  liveBookmanning.com
  Modern CA release operation is a concurrency operation that publishes preceding effects so that a corresponding acquire can observe them.
• 

  liveBookmanning.com
  Modern C, Third EditionRelease semantics are memory-ordering properties that make preceding effects available to a thread that synchronizes with the release operation.

Compare how 4 books explain acquire-release semantics →

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.

This explainer was generated by Manning's knowledge graph from the text of C# Concurrency: Asynchronous and multithreaded programming. The section links point to the parts of the book it draws on.