This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 110d. See for the official list.


785. “Execution sequence” is inappropriate phraseology

Section: 6.9.1  [intro.execution]     Status: CD2     Submitter: US/UK     Date: 3 March, 2009

N2800 comment US 16
N2800 comment UK 8
N2800 comment UK 7

[Voted into WP at October, 2009 meeting.]

In the presence of threads, it is no longer appropriate to characterize the abstract machine as having an “execution sequence.”

Proposed resolution (September, 2009):

  1. Change 6.9.1 [intro.execution] paragraph 3 as follows:

  2. ...An instance of the abstract machine can thus have more than one possible execution sequence for a given program and a given input.
  3. Change 6.9.1 [intro.execution] paragraph 5 as follows:

  4. A conforming implementation executing a well-formed program shall produce the same observable behavior as one of the possible execution sequences executions of the corresponding instance of the abstract machine with the same program and the same input. However, if any such execution sequence contains an undefined operation, this International Standard places no requirement on the implementation executing that program with that input (not even with regard to operations preceding the first undefined operation).
  5. Delete 6.9.1 [intro.execution] paragraph 6, including the footnote:

  6. The observable behavior of the abstract machine is its sequence of reads and writes to volatile data and calls to library I/O functions. [Footnote: An implementation can offer additional library I/O functions as an extension. Implementations that do so should treat calls to those functions as “observable behavior” as well. —end footnote]
  7. Change 6.9.1 [intro.execution] paragraph 9 as follows:

  8. The least requirements on a conforming implementation are:

    These collectively are referred to as the observable behavior of the program. [Note: more stringent correspondences between abstract and actual semantics may be defined by each implementation. —end note]

(Note; this resolution also resolves issue 612.)