Read-modify-write operation
An operation that reads a value from a location, computes or selects an update, and writes the resulting value back to that location.
C++ Concurrency in Action, Second Edition
A read-modify-write operation atomically reads a value, modifies it, and writes the result as one operation.
- How it is used
- Uses atomic read-modify-write operations to update shared values and support synchronization in concurrent data structures.
- How deep it goes
- Explains return values, compare-exchange failures, release sequences, and cache contention through concrete C++ cases.
- Examples
- Uses atomic booleans, pointer arithmetic, a reference-counted lock-free stack, and a contended atomic counter.
- What you can do after
- Evaluate atomic updates by tracing their values, synchronization effects, and possible contention costs.
Read how C++ Concurrency in Action, Second Edition explains read-modify-write operation →
Modern C
A read-modify-write operation atomically reads an object, computes or applies a modification, and writes the resulting value as one indivisible operation.
- How it is used
- Coordinates atomic updates between threads while controlling visibility and synchronization through memory-order semantics.
- How deep it goes
- Distinguishes operation categories and explains explicit memory-order choices, but does not develop their platform-level implementation.
- Examples
- Uses atomic_fetch_add_explicit on an atomic counter and lists exchange, compare-exchange, compound assignment, increment, decrement, and atomic-flag forms.
- What you can do after
- Apply it via atomic_fetch_add_explicit or compare-exchange interfaces with an explicitly selected memory_order value.
Modern C, Third Edition
A read-modify-write operation atomically reads an object, computes or selects a new value, and writes that value as one indivisible operation.
- How it is used
- Coordinates concurrent access by making selected atomic updates indivisible and usable for synchronization.
- How deep it goes
- Defines recognized forms and synchronization behavior, but stops short of implementation-level mechanics.
- Examples
- Uses atomic increment and decrement alongside separate reads and writes of an atomic unsigned object.
- What you can do after
- Evaluate/understand which atomic expressions combine reading and writing, and how those expressions synchronize between threads.
Read how Modern C, Third Edition explains read-modify-write operation →
Related concepts
- atomic operationaddressed by · An atomic operation accesses or updates shared state as an indivisible action with respect to concurrent operations.
- race conditionproduces · A race condition is a concurrency defect in which program behavior or results depend on the relative timing or ordering of interacting operations.
- atomicitykind of · Atomicity is the property that an operation or group of operations takes effect as an indivisible, all-or-nothing unit, without observable partial effects.
- counterused by · A counter is a stateful numeric value that tracks a quantity by changing through operations such as incrementing, decrementing, resetting, or assignment.
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