124 lines
5.2 KiB
C++
124 lines
5.2 KiB
C++
//===- Caching.h - LLVM Local File Cache ------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the CachedFileStream and the localCache function, which
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// simplifies caching files on the local filesystem in a directory whose
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// contents are managed by a CachePruningPolicy.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_CACHING_H
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#define LLVM_SUPPORT_CACHING_H
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/Error.h"
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#include "llvm/Support/MemoryBuffer.h"
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namespace llvm {
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/// This class wraps an output stream for a file. Most clients should just be
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/// able to return an instance of this base class from the stream callback, but
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/// if a client needs to perform some action after the stream is written to,
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/// that can be done by deriving from this class and overriding the destructor
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/// or the commit() method.
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class CachedFileStream {
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public:
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CachedFileStream(std::unique_ptr<raw_pwrite_stream> OS,
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std::string OSPath = "")
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: OS(std::move(OS)), ObjectPathName(OSPath) {}
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/// Must be called exactly once after the writes to OS have been completed
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/// but before the CachedFileStream object is destroyed.
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virtual Error commit() {
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if (Committed)
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return createStringError(make_error_code(std::errc::invalid_argument),
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Twine("CacheStream already committed."));
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Committed = true;
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return Error::success();
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}
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bool Committed = false;
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std::unique_ptr<raw_pwrite_stream> OS;
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std::string ObjectPathName;
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virtual ~CachedFileStream() {
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if (!Committed)
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report_fatal_error("CachedFileStream was not committed.\n");
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}
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};
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/// This type defines the callback to add a file that is generated on the fly.
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///
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/// Stream callbacks must be thread safe.
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using AddStreamFn = std::function<Expected<std::unique_ptr<CachedFileStream>>(
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unsigned Task, const Twine &ModuleName)>;
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/// This is a callable that manages file caching operations. It accepts a task
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/// ID \p Task, a unique key \p Key, and a module name \p ModuleName, and
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/// returns AddStreamFn(). This function determines whether a cache hit or miss
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/// occurs and handles the appropriate actions.
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using FileCacheFunction = std::function<Expected<AddStreamFn>(
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unsigned Task, StringRef Key, const Twine &ModuleName)>;
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/// This type represents a file cache system that manages caching of files.
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/// It encapsulates a caching function and the directory path where the cache is
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/// stored. To request an item from the cache, pass a unique string as the Key.
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/// For hits, the cached file will be added to the link and this function will
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/// return AddStreamFn(). For misses, the cache will return a stream callback
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/// which must be called at most once to produce content for the stream. The
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/// file stream produced by the stream callback will add the file to the link
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/// after the stream is written to. ModuleName is the unique module identifier
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/// for the bitcode module the cache is being checked for.
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///
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/// Clients generally look like this:
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///
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/// if (AddStreamFn AddStream = Cache(Task, Key, ModuleName))
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/// ProduceContent(AddStream);
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///
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/// CacheDirectoryPath stores the directory path where cached files are kept.
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struct FileCache {
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FileCache(FileCacheFunction CacheFn, const std::string &DirectoryPath)
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: CacheFunction(std::move(CacheFn)), CacheDirectoryPath(DirectoryPath) {}
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FileCache() = default;
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Expected<AddStreamFn> operator()(unsigned Task, StringRef Key,
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const Twine &ModuleName) {
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assert(isValid() && "Invalid cache function");
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return CacheFunction(Task, Key, ModuleName);
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}
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const std::string &getCacheDirectoryPath() const {
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return CacheDirectoryPath;
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}
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bool isValid() const { return static_cast<bool>(CacheFunction); }
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private:
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FileCacheFunction CacheFunction = nullptr;
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std::string CacheDirectoryPath;
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};
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/// This type defines the callback to add a pre-existing file (e.g. in a cache).
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///
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/// Buffer callbacks must be thread safe.
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using AddBufferFn = std::function<void(unsigned Task, const Twine &ModuleName,
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std::unique_ptr<MemoryBuffer> MB)>;
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/// Create a local file system cache which uses the given cache name, temporary
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/// file prefix, cache directory and file callback. This function does not
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/// immediately create the cache directory if it does not yet exist; this is
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/// done lazily the first time a file is added. The cache name appears in error
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/// messages for errors during caching. The temporary file prefix is used in the
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/// temporary file naming scheme used when writing files atomically.
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LLVM_ABI Expected<FileCache> localCache(
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const Twine &CacheNameRef, const Twine &TempFilePrefixRef,
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const Twine &CacheDirectoryPathRef,
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AddBufferFn AddBuffer = [](size_t Task, const Twine &ModuleName,
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std::unique_ptr<MemoryBuffer> MB) {});
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} // namespace llvm
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#endif
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