Alexandre wrote:
>> if (wmm->dwStatus == MCI_MODE_PAUSE) continue;
>> if (wmm->dwStatus != MCI_MODE_PLAY) break; but that's not the same.
>> A concurrent thread might change dwStatus to PAUSE right between the 2
>> lines.
>If the code depends on that sort of thing then it's broken.
>If another thread can change dwStatus you need a critical section
>or an interlocked function.
I believe it's not broken:
1. All writers of wmm->dwStatus are already within a critical section
(except at mciOpen time where there's no threading to consider).
2. The player MUST NOT get stuck in a CS while playing.
3. But it must read that variable.
4. I believe Interlocked* is strictly superfluous when only reading, so
I see no value in InterlockedExchange or InterlockedCompareExchange here.
The player must consider dwStatus conceptually "volatile" (without requiring
the broken C keyword). Therefore one has to carefully
think about possible values of (dwStatus == MCI_PLAY || dwStatus == MODE_PAUSE).
The value could switch from PAUSE to PLAY just when evaluating ||.
However, the statement
+ if (wmm->dwStatus == MCI_MODE_STOP || wmm->dwStatus ==
MCI_MODE_NOT_READY)
+ break;
cannot be fooled by interleaved changes.
Regards,
Jörg Höhle
