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| author | Duncan P. N. Exon Smith <dexonsmith@apple.com> | 2017-03-17 22:55:13 +0000 |
|---|---|---|
| committer | Duncan P. N. Exon Smith <dexonsmith@apple.com> | 2017-03-17 22:55:13 +0000 |
| commit | 4c3cdee2a5047d05201424bf9f80b6664619550d (patch) | |
| tree | 29e05bfdeabc3b67f7a99baba973f00b6ce60b27 /unittests/Basic/CMakeLists.txt | |
| parent | 594a067a96498e6e2840d3332f79cb03339b7b78 (diff) | |
Modules: Cache PCMs in memory and avoid a use-after-free
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!
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@298165 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'unittests/Basic/CMakeLists.txt')
| -rw-r--r-- | unittests/Basic/CMakeLists.txt | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/unittests/Basic/CMakeLists.txt b/unittests/Basic/CMakeLists.txt index 3cb3cb8d3c..3a9f34f3d2 100644 --- a/unittests/Basic/CMakeLists.txt +++ b/unittests/Basic/CMakeLists.txt @@ -6,6 +6,7 @@ add_clang_unittest(BasicTests CharInfoTest.cpp DiagnosticTest.cpp FileManagerTest.cpp + MemoryBufferCacheTest.cpp SourceManagerTest.cpp VirtualFileSystemTest.cpp ) |