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//===-Caching.cpp - LLVM Local File Cache ---------------------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file implements the localCache function, which simplifies creating,
// adding to, and querying a local file system cache. localCache takes care of
// periodically pruning older files from the cache using a CachePruningPolicy.
#include "llvm/Support/Caching.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#if !defined(_MSC_VER) && !defined(__MINGW32__)
#include <unistd.h>
#include <io.h>
using namespace llvm;
Expected<FileCache> llvm::localCache(const Twine &CacheNameRef,
const Twine &TempFilePrefixRef,
const Twine &CacheDirectoryPathRef,
AddBufferFn AddBuffer) {
// Create local copies which are safely captured-by-copy in lambdas
SmallString<64> CacheName, TempFilePrefix, CacheDirectoryPath;
return [=](unsigned Task, StringRef Key,
const Twine &ModuleName) -> Expected<AddStreamFn> {
// This choice of file name allows the cache to be pruned (see pruneCache()
// in include/llvm/Support/CachePruning.h).
SmallString<64> EntryPath;
sys::path::append(EntryPath, CacheDirectoryPath, "llvmcache-" + Key);
// First, see if we have a cache hit.
SmallString<64> ResultPath;
Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForRead(
Twine(EntryPath), sys::fs::OF_UpdateAtime, &ResultPath);
std::error_code EC;
if (FDOrErr) {
ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
MemoryBuffer::getOpenFile(*FDOrErr, EntryPath,
if (MBOrErr) {
AddBuffer(Task, ModuleName, std::move(*MBOrErr));
return AddStreamFn();
EC = MBOrErr.getError();
} else {
EC = errorToErrorCode(FDOrErr.takeError());
// On Windows we can fail to open a cache file with a permission denied
// error. This generally means that another process has requested to delete
// the file while it is still open, but it could also mean that another
// process has opened the file without the sharing permissions we need.
// Since the file is probably being deleted we handle it in the same way as
// if the file did not exist at all.
if (EC != errc::no_such_file_or_directory && EC != errc::permission_denied)
return createStringError(EC, Twine("Failed to open cache file ") +
EntryPath + ": " + EC.message() + "\n");
// This file stream is responsible for commiting the resulting file to the
// cache and calling AddBuffer to add it to the link.
struct CacheStream : CachedFileStream {
AddBufferFn AddBuffer;
sys::fs::TempFile TempFile;
std::string ModuleName;
unsigned Task;
CacheStream(std::unique_ptr<raw_pwrite_stream> OS, AddBufferFn AddBuffer,
sys::fs::TempFile TempFile, std::string EntryPath,
std::string ModuleName, unsigned Task)
: CachedFileStream(std::move(OS), std::move(EntryPath)),
AddBuffer(std::move(AddBuffer)), TempFile(std::move(TempFile)),
ModuleName(ModuleName), Task(Task) {}
~CacheStream() {
// TODO: Manually commit rather than using non-trivial destructor,
// allowing to replace report_fatal_errors with a return Error.
// Make sure the stream is closed before committing it.
// Open the file first to avoid racing with a cache pruner.
ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
sys::fs::convertFDToNativeFile(TempFile.FD), ObjectPathName,
/*FileSize=*/-1, /*RequiresNullTerminator=*/false);
if (!MBOrErr)
report_fatal_error(Twine("Failed to open new cache file ") +
TempFile.TmpName + ": " +
MBOrErr.getError().message() + "\n");
// On POSIX systems, this will atomically replace the destination if
// it already exists. We try to emulate this on Windows, but this may
// fail with a permission denied error (for example, if the destination
// is currently opened by another process that does not give us the
// sharing permissions we need). Since the existing file should be
// semantically equivalent to the one we are trying to write, we give
// AddBuffer a copy of the bytes we wrote in that case. We do this
// instead of just using the existing file, because the pruner might
// delete the file before we get a chance to use it.
Error E = TempFile.keep(ObjectPathName);
E = handleErrors(std::move(E), [&](const ECError &E) -> Error {
std::error_code EC = E.convertToErrorCode();
if (EC != errc::permission_denied)
return errorCodeToError(EC);
auto MBCopy = MemoryBuffer::getMemBufferCopy((*MBOrErr)->getBuffer(),
MBOrErr = std::move(MBCopy);
// FIXME: should we consume the discard error?
return Error::success();
if (E)
report_fatal_error(Twine("Failed to rename temporary file ") +
TempFile.TmpName + " to " + ObjectPathName + ": " +
toString(std::move(E)) + "\n");
AddBuffer(Task, ModuleName, std::move(*MBOrErr));
return [=](size_t Task, const Twine &ModuleName)
-> Expected<std::unique_ptr<CachedFileStream>> {
// Create the cache directory if not already done. Doing this lazily
// ensures the filesystem isn't mutated until the cache is.
if (std::error_code EC = sys::fs::create_directories(
CacheDirectoryPath, /*IgnoreExisting=*/true))
return errorCodeToError(EC);
// Write to a temporary to avoid race condition
SmallString<64> TempFilenameModel;
sys::path::append(TempFilenameModel, CacheDirectoryPath,
TempFilePrefix + "-%%%%%%.tmp.o");
Expected<sys::fs::TempFile> Temp = sys::fs::TempFile::create(
TempFilenameModel, sys::fs::owner_read | sys::fs::owner_write);
if (!Temp)
return createStringError(errc::io_error,
toString(Temp.takeError()) + ": " + CacheName +
": Can't get a temporary file");
// This CacheStream will move the temporary file into the cache when done.
return std::make_unique<CacheStream>(
std::make_unique<raw_fd_ostream>(Temp->FD, /* ShouldClose */ false),
AddBuffer, std::move(*Temp), std::string(EntryPath.str()),
ModuleName.str(), Task);