030d7d6daa
This reverts commit r298185, effectively reapplying r298165, after fixing the new unit tests (PR32338). The memory buffer generator doesn't null-terminate the MemoryBuffer it creates; this version of the commit informs getMemBuffer about that to avoid the assert. Original commit message follows: ---- Clang's internal build system for implicit modules uses lock files to ensure that after a process writes a PCM it will read the same one back in (without contention from other -cc1 commands). Since PCMs are read from disk repeatedly while invalidating, building, and importing, the lock is not released quickly. Furthermore, the LockFileManager is not robust in every environment. Other -cc1 commands can stall until timeout (after about eight minutes). This commit changes the lock file from being necessary for correctness to a (possibly dubious) performance hack. The remaining benefit is to reduce duplicate work in competing -cc1 commands which depend on the same module. Follow-up commits will change the internal build system to continue after a timeout, and reduce the timeout. Perhaps we should reconsider blocking at all. This also fixes a use-after-free, when one part of a compilation validates a PCM and starts using it, and another tries to swap out the PCM for something new. The PCMCache is a new type called MemoryBufferCache, which saves memory buffers based on their filename. Its ownership is shared by the CompilerInstance and ModuleManager. - The ModuleManager stores PCMs there that it loads from disk, never touching the disk if the cache is hot. - When modules fail to validate, they're removed from the cache. - When a CompilerInstance is spawned to build a new module, each already-loaded PCM is assumed to be valid, and is frozen to avoid the use-after-free. - Any newly-built module is written directly to the cache to avoid the round-trip to the filesystem, making lock files unnecessary for correctness. Original patch by Manman Ren; most testcases by Adrian Prantl! llvm-svn: 298278
49 lines
1.5 KiB
C++
49 lines
1.5 KiB
C++
//===- MemoryBufferCache.cpp - Cache for loaded memory buffers ------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "clang/Basic/MemoryBufferCache.h"
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#include "llvm/Support/MemoryBuffer.h"
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using namespace clang;
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llvm::MemoryBuffer &
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MemoryBufferCache::addBuffer(llvm::StringRef Filename,
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std::unique_ptr<llvm::MemoryBuffer> Buffer) {
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auto Insertion =
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Buffers.insert({Filename, BufferEntry{std::move(Buffer), NextIndex++}});
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assert(Insertion.second && "Already has a buffer");
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return *Insertion.first->second.Buffer;
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}
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llvm::MemoryBuffer *MemoryBufferCache::lookupBuffer(llvm::StringRef Filename) {
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auto I = Buffers.find(Filename);
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if (I == Buffers.end())
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return nullptr;
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return I->second.Buffer.get();
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}
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bool MemoryBufferCache::isBufferFinal(llvm::StringRef Filename) {
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auto I = Buffers.find(Filename);
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if (I == Buffers.end())
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return false;
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return I->second.Index < FirstRemovableIndex;
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}
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bool MemoryBufferCache::tryToRemoveBuffer(llvm::StringRef Filename) {
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auto I = Buffers.find(Filename);
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assert(I != Buffers.end() && "No buffer to remove...");
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if (I->second.Index < FirstRemovableIndex)
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return true;
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Buffers.erase(I);
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return false;
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}
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void MemoryBufferCache::finalizeCurrentBuffers() { FirstRemovableIndex = NextIndex; }
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