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-exception 6 // 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 of 11 // 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 #else 24 #include <io.h> 25 #endif 26 27 using namespace llvm; 28 29 Expected<FileCache> llvm::localCache(Twine CacheNameRef, 30 Twine TempFilePrefixRef, 31 Twine CacheDirectoryPathRef, 32 AddBufferFn AddBuffer) { 33 34 // Create local copies which are safely captured-by-copy in lambdas 35 SmallString<64> CacheName, TempFilePrefix, CacheDirectoryPath; 36 CacheNameRef.toVector(CacheName); 37 TempFilePrefixRef.toVector(TempFilePrefix); 38 CacheDirectoryPathRef.toVector(CacheDirectoryPath); 39 40 return [=](unsigned Task, StringRef Key) -> Expected<AddStreamFn> { 41 // This choice of file name allows the cache to be pruned (see pruneCache() 42 // in include/llvm/Support/CachePruning.h). 43 SmallString<64> EntryPath; 44 sys::path::append(EntryPath, CacheDirectoryPath, "llvmcache-" + Key); 45 // First, see if we have a cache hit. 46 SmallString<64> ResultPath; 47 Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForRead( 48 Twine(EntryPath), sys::fs::OF_UpdateAtime, &ResultPath); 49 std::error_code EC; 50 if (FDOrErr) { 51 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr = 52 MemoryBuffer::getOpenFile(*FDOrErr, EntryPath, 53 /*FileSize=*/-1, 54 /*RequiresNullTerminator=*/false); 55 sys::fs::closeFile(*FDOrErr); 56 if (MBOrErr) { 57 AddBuffer(Task, std::move(*MBOrErr)); 58 return AddStreamFn(); 59 } 60 EC = MBOrErr.getError(); 61 } else { 62 EC = errorToErrorCode(FDOrErr.takeError()); 63 } 64 65 // On Windows we can fail to open a cache file with a permission denied 66 // error. This generally means that another process has requested to delete 67 // the file while it is still open, but it could also mean that another 68 // process has opened the file without the sharing permissions we need. 69 // Since the file is probably being deleted we handle it in the same way as 70 // if the file did not exist at all. 71 if (EC != errc::no_such_file_or_directory && EC != errc::permission_denied) 72 return createStringError(EC, Twine("Failed to open cache file ") + 73 EntryPath + ": " + EC.message() + "\n"); 74 75 // This file stream is responsible for commiting the resulting file to the 76 // cache and calling AddBuffer to add it to the link. 77 struct CacheStream : CachedFileStream { 78 AddBufferFn AddBuffer; 79 sys::fs::TempFile TempFile; 80 unsigned Task; 81 82 CacheStream(std::unique_ptr<raw_pwrite_stream> OS, AddBufferFn AddBuffer, 83 sys::fs::TempFile TempFile, std::string EntryPath, 84 unsigned Task) 85 : CachedFileStream(std::move(OS), std::move(EntryPath)), 86 AddBuffer(std::move(AddBuffer)), TempFile(std::move(TempFile)), 87 Task(Task) {} 88 89 ~CacheStream() { 90 // TODO: Manually commit rather than using non-trivial destructor, 91 // allowing to replace report_fatal_errors with a return Error. 92 93 // Make sure the stream is closed before committing it. 94 OS.reset(); 95 96 // Open the file first to avoid racing with a cache pruner. 97 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr = 98 MemoryBuffer::getOpenFile( 99 sys::fs::convertFDToNativeFile(TempFile.FD), ObjectPathName, 100 /*FileSize=*/-1, /*RequiresNullTerminator=*/false); 101 if (!MBOrErr) 102 report_fatal_error(Twine("Failed to open new cache file ") + 103 TempFile.TmpName + ": " + 104 MBOrErr.getError().message() + "\n"); 105 106 // On POSIX systems, this will atomically replace the destination if 107 // it already exists. We try to emulate this on Windows, but this may 108 // fail with a permission denied error (for example, if the destination 109 // is currently opened by another process that does not give us the 110 // sharing permissions we need). Since the existing file should be 111 // semantically equivalent to the one we are trying to write, we give 112 // AddBuffer a copy of the bytes we wrote in that case. We do this 113 // instead of just using the existing file, because the pruner might 114 // delete the file before we get a chance to use it. 115 Error E = TempFile.keep(ObjectPathName); 116 E = handleErrors(std::move(E), [&](const ECError &E) -> Error { 117 std::error_code EC = E.convertToErrorCode(); 118 if (EC != errc::permission_denied) 119 return errorCodeToError(EC); 120 121 auto MBCopy = MemoryBuffer::getMemBufferCopy((*MBOrErr)->getBuffer(), 122 ObjectPathName); 123 MBOrErr = std::move(MBCopy); 124 125 // FIXME: should we consume the discard error? 126 consumeError(TempFile.discard()); 127 128 return Error::success(); 129 }); 130 131 if (E) 132 report_fatal_error(Twine("Failed to rename temporary file ") + 133 TempFile.TmpName + " to " + ObjectPathName + ": " + 134 toString(std::move(E)) + "\n"); 135 136 AddBuffer(Task, std::move(*MBOrErr)); 137 } 138 }; 139 140 return [=](size_t Task) -> Expected<std::unique_ptr<CachedFileStream>> { 141 // Create the cache directory if not already done. Doing this lazily 142 // ensures the filesystem isn't mutated until the cache is. 143 if (std::error_code EC = sys::fs::create_directories( 144 CacheDirectoryPath, /*IgnoreExisting=*/true)) 145 return errorCodeToError(EC); 146 147 // Write to a temporary to avoid race condition 148 SmallString<64> TempFilenameModel; 149 sys::path::append(TempFilenameModel, CacheDirectoryPath, 150 TempFilePrefix + "-%%%%%%.tmp.o"); 151 Expected<sys::fs::TempFile> Temp = sys::fs::TempFile::create( 152 TempFilenameModel, sys::fs::owner_read | sys::fs::owner_write); 153 if (!Temp) 154 return createStringError(errc::io_error, 155 toString(Temp.takeError()) + ": " + CacheName + 156 ": Can't get a temporary file"); 157 158 // This CacheStream will move the temporary file into the cache when done. 159 return std::make_unique<CacheStream>( 160 std::make_unique<raw_fd_ostream>(Temp->FD, /* ShouldClose */ false), 161 AddBuffer, std::move(*Temp), std::string(EntryPath.str()), Task); 162 }; 163 }; 164 } 165