The C11 and C++11 Concurrency Model

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sublanguages and the related parts of the model that each section introduces:
Section sublanguage
elements of model introduced
§3.1 single threaded (no locks, no atomics, no
fences)
top-level model structure, sequenced-before
§3.2 concurrent with locks lock-order, synchronises-with, data races
§3.3 concurrent with relaxed atomics and locks atomics, modification order, coherence, CAS
§3.4 concurrent with release and acquire atomics
and locks (no relaxed atomics)
release-acquire synchronisation
§3.5 release, acquire and relaxed atomics and locks release sequences
§3.6 all of the above plus release and acquire fences hypothetical release sequences
§3.7 all of the above plus SC atomics SC-order
§3.8 all of the above plus SC fences SC fence restrictions
§3.9 all of the above plus consume atomics (locks,
all atomics, all fences)
data-dependence, carries-a-dependency-to,
dependency-ordered-before
§3.10 locks, all atomics, all fences visible-sequences-of-side-effects
3.1 Top-level structure by example: single-threaded programs
Before introducing the memory model that governs simple single-threaded programs, it is
necessary to formally define the top-level structure and underlying types of the memory
model. We start with the type of actions.
Memory actions Reads and writes to memory, locks, unlocks and fences are modelled
by memory events called actions. The action type is given below. Each action has a
unique action-identifier, of type aid, and a thread identifier, of type tid, identifying its
host thread.
type action =
| Lock of aid ∗ tid ∗ location ∗ lock outcome
| Unlock of aid ∗ tid ∗ location
| Load of aid ∗ tid ∗ memory order ∗ location ∗ cvalue
| Store of aid ∗ tid ∗ memory order ∗ location ∗ cvalue
| RMW of aid ∗ tid ∗ memory order ∗ location ∗ cvalue ∗ cvalue
| Fence of aid ∗ tid ∗ memory order
| Blocked rmw of aid ∗ tid ∗ location
Locks have an outcome and can either leave the mutex Locked or Blocked:
type lock outcome =
Locked
| Blocked