Sequenced-before relation
The sequenced-before relation is an ordering relation between evaluations within a single thread, as determined by the programming language’s execution rules.
C++ Concurrency in Action, Second Edition
A C++ ordering relation between evaluations within a single thread.
- How it is used
- Uses single-thread evaluation order to establish happens-before guarantees across threads through synchronization.
- How deep it goes
- Explains statement and expression ordering, then traces its composition with synchronization and acquire-release operations.
- Examples
- Uses function arguments with unspecified evaluation order and a spinlock protecting shared data.
- What you can do after
- Evaluate when operations are ordered within a thread and how that order carries across a synchronization boundary.
Read how C++ Concurrency in Action, Second Edition explains sequenced-before relation →
Modern C
The sequenced-before relation orders evaluations within a thread according to the C program's execution rules.
- How it is used
- Orders evaluations within one thread when reasoning about execution, correctness, and the consistency of observations.
- How deep it goes
- Defines the relation through a happened-before rule and a switch example, but defers cross-thread ordering to synchronization.
- Examples
- Uses a command[0] assignment before a switch and nested calls below ungetc to show an updated value being observed.
- What you can do after
- Evaluate within-thread ordering and determine when a later statement observes an earlier assignment.
Related concepts
- happens-before relationpart of · A happens-before relation is a partial ordering between events that establishes when one causally precedes another for reasoning about execution and effects.
- relationkind of · A relation is a rule or set of associations that links elements of one set with elements of another set without requiring unique outputs.
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