Modification order
Modification order is the total order of modifications to a particular atomic object, consistent with the sequenced-before order of each participating thread.
C++ Concurrency in Action, Second Edition
A per-object order of all writes to that object, including its initialization, on which all threads in a given execution must agree.
- How it is used
- Defines the per-object agreement used to reason about writes and atomic reads across threads.
- How deep it goes
- Explains initialization, thread agreement, read constraints, and the limit of per-object ordering; leaves cross-object guarantees to memory-order rules.
- Examples
- Contrasts relaxed atomic flag reads that can miss an earlier write with acquire-release flag reads that order it.
- What you can do after
- Diagnose/debug with it why atomic reads can disagree about operations on different objects without reversing either object's modification order.
Read how C++ Concurrency in Action, Second Edition explains modification order →
Modern C, Third Edition
Modification order is the total order of modifications to a particular atomic object that is consistent with each participating thread's sequenced-before order.
- How it is used
- Uses atomic objects to reason about cross-thread visibility, synchronization, and the ordering of competing writes.
- How deep it goes
- Defines per-object ordering and contrasts it with sequential consistency, but does not develop a full formal memory-model derivation.
- Examples
- Uses a shared atomic x initialized to 11, threaded increments, decrements, assignments, reads, and a synchronization diagram.
- What you can do after
- Evaluate/understand how atomic reads and writes can be ordered consistently and when stronger global ordering is required.
Read how Modern C, Third Edition explains modification order →
Modern C
Modification order is the single order of all modifications to a particular atomic object that is consistent with each participating thread's sequenced-before order.
- How it is used
- Explains how threads perceive changes to one atomic object and how atomic operations provide synchronization.
- How deep it goes
- Defines the per-object order, illustrates six modifications, and contrasts it with sequential consistency’s global order across atomic objects.
- Examples
- Uses atomic x with initialization to 11, two increments, three assignments, and cross-thread reads that establish synchronization.
- What you can do after
- Evaluate whether atomic operations require per-object ordering or sequentially consistent global ordering.
Related concepts
- sequential consistencyproduced by · Sequential consistency is a memory model in which participating operations appear in a single total order that preserves each thread’s program order.
- atomic typeused by · An atomic type is a type whose supported accesses and operations are indivisible with respect to concurrent execution and provide defined synchronization semantics.
- speculative executioncontrasts with · Speculative execution is a processor technique that performs predicted work before its need or correctness is confirmed, discarding results if the prediction is wrong.
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