Reapply "Modules: Cache PCMs in memory and avoid a use-after-free"
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
diff --git a/clang/unittests/Lex/LexerTest.cpp b/clang/unittests/Lex/LexerTest.cpp
index 918167b..b5a6fd9 100644
--- a/clang/unittests/Lex/LexerTest.cpp
+++ b/clang/unittests/Lex/LexerTest.cpp
@@ -12,6 +12,7 @@
#include "clang/Basic/DiagnosticOptions.h"
#include "clang/Basic/FileManager.h"
#include "clang/Basic/LangOptions.h"
+#include "clang/Basic/MemoryBufferCache.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Basic/TargetOptions.h"
@@ -64,10 +65,12 @@
SourceMgr.setMainFileID(SourceMgr.createFileID(std::move(Buf)));
VoidModuleLoader ModLoader;
+ MemoryBufferCache PCMCache;
HeaderSearch HeaderInfo(std::make_shared<HeaderSearchOptions>(), SourceMgr,
Diags, LangOpts, Target.get());
Preprocessor PP(std::make_shared<PreprocessorOptions>(), Diags, LangOpts,
- SourceMgr, HeaderInfo, ModLoader, /*IILookup =*/nullptr,
+ SourceMgr, PCMCache, HeaderInfo, ModLoader,
+ /*IILookup =*/nullptr,
/*OwnsHeaderSearch =*/false);
PP.Initialize(*Target);
PP.EnterMainSourceFile();