forked from OSchip/llvm-project
079c40e886
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: 298165
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| .. | ||
| ARCMT | ||
| ASTMerge | ||
| Analysis | ||
| CXX | ||
| CodeCompletion | ||
| CodeGen | ||
| CodeGenCUDA | ||
| CodeGenCXX | ||
| CodeGenCoroutines | ||
| CodeGenObjC | ||
| CodeGenObjCXX | ||
| CodeGenOpenCL | ||
| Coverage | ||
| CoverageMapping | ||
| Driver | ||
| FixIt | ||
| Format | ||
| Frontend | ||
| Headers | ||
| Import | ||
| Index | ||
| Integration | ||
| Layout | ||
| Lexer | ||
| Misc | ||
| Modules | ||
| OpenMP | ||
| PCH | ||
| Parser | ||
| Preprocessor | ||
| Profile | ||
| Rewriter | ||
| Sema | ||
| SemaCUDA | ||
| SemaCXX | ||
| SemaObjC | ||
| SemaObjCXX | ||
| SemaOpenCL | ||
| SemaTemplate | ||
| TableGen | ||
| Tooling | ||
| Unit | ||
| VFS | ||
| .clang-format | ||
| CMakeLists.txt | ||
| TestRunner.sh | ||
| cxx-sections.data | ||
| lit.cfg | ||
| lit.site.cfg.in | ||
| make_test_dirs.pl | ||