Sequential consistency
Sequential consistency is a memory model in which participating operations appear in a single total order that preserves each thread’s program order.
C++ Concurrency in Action, Second Edition
Sequentially consistent ordering requires atomic operations using that ordering to fit one total order consistent with each thread's program order.
- How it is used
- Provides the default, easier-to-reason-about ordering for C++ atomic operations.
- How deep it goes
- Works through a four-thread total-order argument and compares guarantees and costs, without detailing CPU instruction sequences.
- Examples
- Uses two atomic flags, two waiting readers, and an assertion that at least one reader sees both flags set.
- What you can do after
- Evaluate/understand whether sequentially consistent atomic operations rule out a proposed four-thread observation.
Read how C++ Concurrency in Action, Second Edition explains sequential consistency →
Modern C
Sequential consistency is a memory-consistency model in which all operations on atomic objects appear in one global order consistent with each thread's program order.
- How it is used
- Uses a strong ordering model to reason about synchronization and the observable order of concurrent atomic operations.
- How deep it goes
- Explains global linearization, acquire-release implications, C interfaces, and performance costs without developing every implementation detail.
- Examples
- Uses a two-thread atomic-synchronization figure and declarations for ordinary and explicit C atomic interfaces.
- What you can do after
- Operate/configure C atomic operations using default sequential consistency or memory_order_seq_cst through _explicit interfaces.
Related concepts
- memory orderingconfigured by · Memory ordering is the set of rules governing the permitted ordering and visibility of memory operations across concurrent execution contexts.
- consistency modelkind of · A consistency model is a formal specification of how operations on state may be ordered and what values those operations can observe.
- acquire-release semanticscontrasts with · Acquire-release semantics are memory-ordering rules under which release operations make preceding effects visible to acquire operations that synchronize with them.
- modification orderproduces · Modification order is the total order of modifications to a particular atomic object, consistent with the sequenced-before order of each participating thread.
- atomicityconfigures · Atomicity is the property that an operation or group of operations takes effect as an indivisible, all-or-nothing unit, without observable partial effects.
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