llvm/llvm/include/llvm/Support/Caching.h

//===- Caching.h - LLVM Local File Cache ------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines the CachedFileStream and the localCache function, which
// simplifies caching files on the local filesystem in a directory whose
// contents are managed by a CachePruningPolicy.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_SUPPORT_CACHING_H
#define LLVM_SUPPORT_CACHING_H

#include "llvm/Support/Error.h"

namespace llvm {

class MemoryBuffer;

/// This class wraps an output stream for a file. Most clients should just be
/// able to return an instance of this base class from the stream callback, but
/// if a client needs to perform some action after the stream is written to,
/// that can be done by deriving from this class and overriding the destructor.
class CachedFileStream { … };

/// This type defines the callback to add a file that is generated on the fly.
///
/// Stream callbacks must be thread safe.
AddStreamFn;

/// This is a callable that manages file caching operations. It accepts a task
/// ID \p Task, a unique key \p Key, and a module name \p ModuleName, and
/// returns AddStreamFn(). This function determines whether a cache hit or miss
/// occurs and handles the appropriate actions.
FileCacheFunction;

/// This type represents a file cache system that manages caching of files.
/// It encapsulates a caching function and the directory path where the cache is
/// stored. To request an item from the cache, pass a unique string as the Key.
/// For hits, the cached file will be added to the link and this function will
/// return AddStreamFn(). For misses, the cache will return a stream callback
/// which must be called at most once to produce content for the stream. The
/// file stream produced by the stream callback will add the file to the link
/// after the stream is written to. ModuleName is the unique module identifier
/// for the bitcode module the cache is being checked for.
///
/// Clients generally look like this:
///
/// if (AddStreamFn AddStream = Cache(Task, Key, ModuleName))
///   ProduceContent(AddStream);
///
/// CacheDirectoryPath stores the directory path where cached files are kept.
struct FileCache { … };

/// This type defines the callback to add a pre-existing file (e.g. in a cache).
///
/// Buffer callbacks must be thread safe.
AddBufferFn;

/// Create a local file system cache which uses the given cache name, temporary
/// file prefix, cache directory and file callback.  This function does not
/// immediately create the cache directory if it does not yet exist; this is
/// done lazily the first time a file is added.  The cache name appears in error
/// messages for errors during caching. The temporary file prefix is used in the
/// temporary file naming scheme used when writing files atomically.
Expected<FileCache> localCache(
    const Twine &CacheNameRef, const Twine &TempFilePrefixRef,
    const Twine &CacheDirectoryPathRef,
    AddBufferFn AddBuffer = [](size_t Task, const Twine &ModuleName,
                               std::unique_ptr<MemoryBuffer> MB) {});
} // namespace llvm

#endif