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 = 42 std::function<Expected<std::unique_ptr<CachedFileStream>>(unsigned Task)>; 43 44 /// This is the type of a file cache. To request an item from the cache, pass a 45 /// unique string as the Key. For hits, the cached file will be added to the 46 /// link and this function will return AddStreamFn(). For misses, the cache will 47 /// return a stream callback which must be called at most once to produce 48 /// content for the stream. The file stream produced by the stream callback will 49 /// add the file to the link after the stream is written to. 50 /// 51 /// Clients generally look like this: 52 /// 53 /// if (AddStreamFn AddStream = Cache(Task, Key)) 54 /// ProduceContent(AddStream); 55 using FileCache = 56 std::function<Expected<AddStreamFn>(unsigned Task, StringRef Key)>; 57 58 /// This type defines the callback to add a pre-existing file (e.g. in a cache). 59 /// 60 /// Buffer callbacks must be thread safe. 61 using AddBufferFn = 62 std::function<void(unsigned Task, std::unique_ptr<MemoryBuffer> MB)>; 63 64 /// Create a local file system cache which uses the given cache name, temporary 65 /// file prefix, cache directory and file callback. This function does not 66 /// immediately create the cache directory if it does not yet exist; this is 67 /// done lazily the first time a file is added. The cache name appears in error 68 /// messages for errors during caching. The temporary file prefix is used in the 69 /// temporary file naming scheme used when writing files atomically. 70 Expected<FileCache> localCache( 71 Twine CacheNameRef, Twine TempFilePrefixRef, Twine CacheDirectoryPathRef, 72 AddBufferFn AddBuffer = [](size_t Task, std::unique_ptr<MemoryBuffer> MB) { 73 }); 74 } // namespace llvm 75 76 #endif 77