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Improve documentation of thread- and exception-safety precautions.

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 Change: 183635
 ServerID: perforce.ravenbrook.com
This commit is contained in:
Gareth Rees 2013-11-04 15:14:47 +00:00
parent ba0e8c1b8b
commit 73fa242bb1
1 changed files with 16 additions and 3 deletions
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19
mps/code/global.c
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@ -518,6 +518,10 @@ void arenaEnterLock(Arena arena, int recursive)
the client if so. */
AVER(TESTT(Arena, arena));
/* It's critical that the stack probe is outside the lock, because
* the stack probe may cause arbitrary code to run (via a signal or
* exception handler) and that code may enter the MPS. If we took
* the lock first then this would deadlock. */
StackProbe(StackProbeDEPTH);
lock = ArenaGlobals(arena)->lock;
if(recursive) {
@ -626,13 +630,17 @@ Bool ArenaAccess(Addr addr, AccessSet mode, MutatorFaultContext context)
if (SegOfAddr(&seg, arena, addr)) {
mps_exception_info = NULL;
arenaReleaseRingLock();
/* An access in a different thread may have already caused the
* protection to be cleared. This avoids calling TraceAccess on
* protection that has already been cleared on a separate thread. */
/* An access in a different thread (or even in the same thread,
* via a signal or exception handler) may have already caused
* the protection to be cleared. This avoids calling TraceAccess
* on protection that has already been cleared on a separate
* thread. */
mode &= SegPM(seg);
if (mode != AccessSetEMPTY) {
res = PoolAccess(SegPool(seg), seg, addr, mode, context);
AVER(res == ResOK); /* Mutator can't continue unless this succeeds */
} else {
/* Protection was already cleared: nothing to do now. */
}
EVENT4(ArenaAccess, arena, count, addr, mode);
ArenaLeave(arena);
@ -646,6 +654,11 @@ Bool ArenaAccess(Addr addr, AccessSet mode, MutatorFaultContext context)
EVENT4(ArenaAccess, arena, count, addr, mode);
ArenaLeave(arena);
return TRUE;
} else {
/* No segment or root was found at the address: this must mean
* that activity in another thread (or even in the same thread,
* via a signal or exception handler) caused the segment or root
* to go away. So there's nothing to do now. */
}
ArenaLeave(arena);