1 //===- Caching.h - LLVM Local File Cache ------------------------*- C++ -*-===// 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 defines the CachedFileStream and the localCache function, which 10 // simplifies caching files on the local filesystem in a directory whose 11 // contents are managed by a CachePruningPolicy. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_SUPPORT_CACHING_H 16 #define LLVM_SUPPORT_CACHING_H 17 18 #include "llvm/Support/Error.h" 19 20 namespace llvm { 21 22 class MemoryBuffer; 23 24 /// This class wraps an output stream for a file. Most clients should just be 25 /// able to return an instance of this base class from the stream callback, but 26 /// if a client needs to perform some action after the stream is written to, 27 /// that can be done by deriving from this class and overriding the destructor. 28 class CachedFileStream { 29 public: 30 CachedFileStream(std::unique_ptr<raw_pwrite_stream> OS, 31 std::string OSPath = "") 32 : OS(std::move(OS)), ObjectPathName(OSPath) {} 33 std::unique_ptr<raw_pwrite_stream> OS; 34 std::string ObjectPathName; 35 virtual ~CachedFileStream() = default; 36 }; 37 38 /// This type defines the callback to add a file that is generated on the fly. 39 /// 40 /// Stream callbacks must be thread safe. 41 using AddStreamFn = std::function<Expected<std::unique_ptr<CachedFileStream>>( 42 unsigned Task, const Twine &ModuleName)>; 43 44 /// This is a callable that manages file caching operations. It accepts a task 45 /// ID \p Task, a unique key \p Key, and a module name \p ModuleName, and 46 /// returns AddStreamFn(). This function determines whether a cache hit or miss 47 /// occurs and handles the appropriate actions. 48 using FileCacheFunction = std::function<Expected<AddStreamFn>( 49 unsigned Task, StringRef Key, const Twine &ModuleName)>; 50 51 /// This type represents a file cache system that manages caching of files. 52 /// It encapsulates a caching function and the directory path where the cache is 53 /// stored. To request an item from the cache, pass a unique string as the Key. 54 /// For hits, the cached file will be added to the link and this function will 55 /// return AddStreamFn(). For misses, the cache will return a stream callback 56 /// which must be called at most once to produce content for the stream. The 57 /// file stream produced by the stream callback will add the file to the link 58 /// after the stream is written to. ModuleName is the unique module identifier 59 /// for the bitcode module the cache is being checked for. 60 /// 61 /// Clients generally look like this: 62 /// 63 /// if (AddStreamFn AddStream = Cache(Task, Key, ModuleName)) 64 /// ProduceContent(AddStream); 65 /// 66 /// CacheDirectoryPath stores the directory path where cached files are kept. 67 struct FileCache { 68 FileCache(FileCacheFunction CacheFn, const std::string &DirectoryPath) 69 : CacheFunction(std::move(CacheFn)), CacheDirectoryPath(DirectoryPath) {} 70 FileCache() = default; 71 72 Expected<AddStreamFn> operator()(unsigned Task, StringRef Key, 73 const Twine &ModuleName) { 74 assert(isValid() && "Invalid cache function"); 75 return CacheFunction(Task, Key, ModuleName); 76 } 77 const std::string &getCacheDirectoryPath() const { 78 return CacheDirectoryPath; 79 } 80 bool isValid() const { return static_cast<bool>(CacheFunction); } 81 82 private: 83 FileCacheFunction CacheFunction = nullptr; 84 std::string CacheDirectoryPath; 85 }; 86 87 /// This type defines the callback to add a pre-existing file (e.g. in a cache). 88 /// 89 /// Buffer callbacks must be thread safe. 90 using AddBufferFn = std::function<void(unsigned Task, const Twine &ModuleName, 91 std::unique_ptr<MemoryBuffer> MB)>; 92 93 /// Create a local file system cache which uses the given cache name, temporary 94 /// file prefix, cache directory and file callback. This function does not 95 /// immediately create the cache directory if it does not yet exist; this is 96 /// done lazily the first time a file is added. The cache name appears in error 97 /// messages for errors during caching. The temporary file prefix is used in the 98 /// temporary file naming scheme used when writing files atomically. 99 Expected<FileCache> localCache( 100 const Twine &CacheNameRef, const Twine &TempFilePrefixRef, 101 const Twine &CacheDirectoryPathRef, 102 AddBufferFn AddBuffer = [](size_t Task, const Twine &ModuleName, 103 std::unique_ptr<MemoryBuffer> MB) {}); 104 } // namespace llvm 105 106 #endif 107