177 lines · cpp
1//===-Caching.cpp - LLVM Local File Cache ---------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8//9// This file implements the localCache function, which simplifies creating,10// adding to, and querying a local file system cache. localCache takes care of11// periodically pruning older files from the cache using a CachePruningPolicy.12//13//===----------------------------------------------------------------------===//14 15#include "llvm/Support/Caching.h"16#include "llvm/Support/Errc.h"17#include "llvm/Support/FileSystem.h"18#include "llvm/Support/MemoryBuffer.h"19#include "llvm/Support/Path.h"20 21#if !defined(_MSC_VER) && !defined(__MINGW32__)22#include <unistd.h>23#else24#include <io.h>25#endif26 27using namespace llvm;28 29Expected<FileCache> llvm::localCache(const Twine &CacheNameRef,30 const Twine &TempFilePrefixRef,31 const Twine &CacheDirectoryPathRef,32 AddBufferFn AddBuffer) {33 34 // Create local copies which are safely captured-by-copy in lambdas35 SmallString<64> CacheName, TempFilePrefix, CacheDirectoryPath;36 CacheNameRef.toVector(CacheName);37 TempFilePrefixRef.toVector(TempFilePrefix);38 CacheDirectoryPathRef.toVector(CacheDirectoryPath);39 40 auto Func = [=](unsigned Task, StringRef Key,41 const Twine &ModuleName) -> Expected<AddStreamFn> {42 // This choice of file name allows the cache to be pruned (see pruneCache()43 // in include/llvm/Support/CachePruning.h).44 SmallString<64> EntryPath;45 sys::path::append(EntryPath, CacheDirectoryPath, "llvmcache-" + Key);46 // First, see if we have a cache hit.47 SmallString<64> ResultPath;48 Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForRead(49 Twine(EntryPath), sys::fs::OF_UpdateAtime, &ResultPath);50 std::error_code EC;51 if (FDOrErr) {52 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =53 MemoryBuffer::getOpenFile(*FDOrErr, EntryPath,54 /*FileSize=*/-1,55 /*RequiresNullTerminator=*/false);56 sys::fs::closeFile(*FDOrErr);57 if (MBOrErr) {58 AddBuffer(Task, ModuleName, std::move(*MBOrErr));59 return AddStreamFn();60 }61 EC = MBOrErr.getError();62 } else {63 EC = errorToErrorCode(FDOrErr.takeError());64 }65 66 // On Windows we can fail to open a cache file with a permission denied67 // error. This generally means that another process has requested to delete68 // the file while it is still open, but it could also mean that another69 // process has opened the file without the sharing permissions we need.70 // Since the file is probably being deleted we handle it in the same way as71 // if the file did not exist at all.72 if (EC != errc::no_such_file_or_directory && EC != errc::permission_denied)73 return createStringError(EC, Twine("Failed to open cache file ") +74 EntryPath + ": " + EC.message() + "\n");75 76 // This file stream is responsible for commiting the resulting file to the77 // cache and calling AddBuffer to add it to the link.78 struct CacheStream : CachedFileStream {79 AddBufferFn AddBuffer;80 sys::fs::TempFile TempFile;81 std::string ModuleName;82 unsigned Task;83 84 CacheStream(std::unique_ptr<raw_pwrite_stream> OS, AddBufferFn AddBuffer,85 sys::fs::TempFile TempFile, std::string EntryPath,86 std::string ModuleName, unsigned Task)87 : CachedFileStream(std::move(OS), std::move(EntryPath)),88 AddBuffer(std::move(AddBuffer)), TempFile(std::move(TempFile)),89 ModuleName(ModuleName), Task(Task) {}90 91 Error commit() override {92 Error E = CachedFileStream::commit();93 if (E)94 return E;95 96 // Make sure the stream is closed before committing it.97 OS.reset();98 99 // Open the file first to avoid racing with a cache pruner.100 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =101 MemoryBuffer::getOpenFile(102 sys::fs::convertFDToNativeFile(TempFile.FD), ObjectPathName,103 /*FileSize=*/-1, /*RequiresNullTerminator=*/false);104 if (!MBOrErr) {105 std::error_code EC = MBOrErr.getError();106 return createStringError(EC, Twine("Failed to open new cache file ") +107 TempFile.TmpName + ": " +108 EC.message() + "\n");109 }110 111 // On POSIX systems, this will atomically replace the destination if112 // it already exists. We try to emulate this on Windows, but this may113 // fail with a permission denied error (for example, if the destination114 // is currently opened by another process that does not give us the115 // sharing permissions we need). Since the existing file should be116 // semantically equivalent to the one we are trying to write, we give117 // AddBuffer a copy of the bytes we wrote in that case. We do this118 // instead of just using the existing file, because the pruner might119 // delete the file before we get a chance to use it.120 E = TempFile.keep(ObjectPathName);121 E = handleErrors(std::move(E), [&](const ECError &E) -> Error {122 std::error_code EC = E.convertToErrorCode();123 if (EC != errc::permission_denied)124 return createStringError(125 EC, Twine("Failed to rename temporary file ") +126 TempFile.TmpName + " to " + ObjectPathName + ": " +127 EC.message() + "\n");128 129 auto MBCopy = MemoryBuffer::getMemBufferCopy((*MBOrErr)->getBuffer(),130 ObjectPathName);131 MBOrErr = std::move(MBCopy);132 133 // FIXME: should we consume the discard error?134 consumeError(TempFile.discard());135 136 return Error::success();137 });138 139 if (E)140 return E;141 142 AddBuffer(Task, ModuleName, std::move(*MBOrErr));143 return Error::success();144 }145 };146 147 return [=](size_t Task, const Twine &ModuleName)148 -> Expected<std::unique_ptr<CachedFileStream>> {149 // Create the cache directory if not already done. Doing this lazily150 // ensures the filesystem isn't mutated until the cache is.151 if (std::error_code EC = sys::fs::create_directories(152 CacheDirectoryPath, /*IgnoreExisting=*/true))153 return createStringError(EC, Twine("can't create cache directory ") +154 CacheDirectoryPath + ": " +155 EC.message());156 157 // Write to a temporary to avoid race condition158 SmallString<64> TempFilenameModel;159 sys::path::append(TempFilenameModel, CacheDirectoryPath,160 TempFilePrefix + "-%%%%%%.tmp.o");161 Expected<sys::fs::TempFile> Temp = sys::fs::TempFile::create(162 TempFilenameModel, sys::fs::owner_read | sys::fs::owner_write);163 if (!Temp)164 return createStringError(errc::io_error,165 toString(Temp.takeError()) + ": " + CacheName +166 ": Can't get a temporary file");167 168 // This CacheStream will move the temporary file into the cache when done.169 return std::make_unique<CacheStream>(170 std::make_unique<raw_fd_ostream>(Temp->FD, /* ShouldClose */ false),171 AddBuffer, std::move(*Temp), std::string(EntryPath), ModuleName.str(),172 Task);173 };174 };175 return FileCache(Func, CacheDirectoryPathRef.str());176}177