From 6bb26dafa4cda63c14da97e65eff1e982375fd16 Mon Sep 17 00:00:00 2001 From: Reid Kleckner Date: Thu, 11 Jun 2015 22:22:45 +0000 Subject: [PATCH] [Support] Fix a race initializing a static local in MSVC 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. llvm-svn: 239566 --- llvm/lib/Support/Windows/Memory.inc | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/llvm/lib/Support/Windows/Memory.inc b/llvm/lib/Support/Windows/Memory.inc index ae8371abf5b3..4b2ff2e2d324 100644 --- a/llvm/lib/Support/Windows/Memory.inc +++ b/llvm/lib/Support/Windows/Memory.inc @@ -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(NearBlock->base()) +