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[Support] Fix a race initializing a static local in MSVC

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static local initialization isn't thread safe with MSVC and a race was
reported in PR23817. We can't use std::atomic because it's not trivially
constructible, so instead do some lame volatile global integer
manipulation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239566 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Kleckner 2015-06-11 22:22:45 +00:00
parent 68e51493f7
commit 5e9819c5bd
1 changed files with 9 additions and 1 deletions
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10
lib/Support/Windows/Memory.inc
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@ -78,7 +78,15 @@ MemoryBlock Memory::allocateMappedMemory(size_t NumBytes,
// While we'd be happy to allocate single pages, the Windows allocation
// granularity may be larger than a single page (in practice, it is 64K)
// so mapping less than that will create an unreachable fragment of memory.
static const size_t Granularity = getAllocationGranularity();
// Avoid using one-time initialization of static locals here, since they
// aren't thread safe with MSVC.
static volatile size_t GranularityCached;
size_t Granularity = GranularityCached;
if (Granularity == 0) {
Granularity = getAllocationGranularity();
GranularityCached = Granularity;
}
const size_t NumBlocks = (NumBytes+Granularity-1)/Granularity;
uintptr_t Start = NearBlock ? reinterpret_cast<uintptr_t>(NearBlock->base()) +