1//===-Caching.cpp - LLVM Local File Cache ---------------------------------===//
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 implements the localCache function, which simplifies creating,
10// adding to, and querying a local file system cache. localCache takes care of
11// periodically pruning older files from the cache using a CachePruningPolicy.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/Support/Caching.h"
16#include "llvm/Support/Errc.h"
17#include "llvm/Support/FileSystem.h"
18#include "llvm/Support/MemoryBuffer.h"
19#include "llvm/Support/Path.h"
20
21#if !defined(_MSC_VER) && !defined(__MINGW32__)
22#include <unistd.h>
23#else
24#include <io.h>
25#endif
26
27using namespace llvm;
28
29Expected<FileCache> llvm::localCache(const Twine &CacheNameRef,
30 const Twine &TempFilePrefixRef,
31 const Twine &CacheDirectoryPathRef,
32 AddBufferFn AddBuffer) {
33
34 // Create local copies which are safely captured-by-copy in lambdas
35 SmallString<64> CacheName, TempFilePrefix, CacheDirectoryPath;
36 CacheNameRef.toVector(Out&: CacheName);
37 TempFilePrefixRef.toVector(Out&: TempFilePrefix);
38 CacheDirectoryPathRef.toVector(Out&: CacheDirectoryPath);
39
40 auto Func = [=](unsigned Task, StringRef Key,
41 const Twine &ModuleName) -> Expected<AddStreamFn> {
42 // This choice of file name allows the cache to be pruned (see pruneCache()
43 // in include/llvm/Support/CachePruning.h).
44 SmallString<64> EntryPath;
45 sys::path::append(path&: EntryPath, a: CacheDirectoryPath, b: "llvmcache-" + Key);
46 // First, see if we have a cache hit.
47 SmallString<64> ResultPath;
48 Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForRead(
49 Name: Twine(EntryPath), Flags: sys::fs::OF_UpdateAtime, RealPath: &ResultPath);
50 std::error_code EC;
51 if (FDOrErr) {
52 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
53 MemoryBuffer::getOpenFile(FD: *FDOrErr, Filename: EntryPath,
54 /*FileSize=*/-1,
55 /*RequiresNullTerminator=*/false);
56 sys::fs::closeFile(F&: *FDOrErr);
57 if (MBOrErr) {
58 AddBuffer(Task, ModuleName, std::move(*MBOrErr));
59 return AddStreamFn();
60 }
61 EC = MBOrErr.getError();
62 } else {
63 EC = errorToErrorCode(Err: FDOrErr.takeError());
64 }
65
66 // On Windows we can fail to open a cache file with a permission denied
67 // error. This generally means that another process has requested to delete
68 // the file while it is still open, but it could also mean that another
69 // process has opened the file without the sharing permissions we need.
70 // Since the file is probably being deleted we handle it in the same way as
71 // if the file did not exist at all.
72 if (EC != errc::no_such_file_or_directory && EC != errc::permission_denied)
73 return createStringError(EC, S: Twine("Failed to open cache file ") +
74 EntryPath + ": " + EC.message() + "\n");
75
76 // This file stream is responsible for commiting the resulting file to the
77 // cache and calling AddBuffer to add it to the link.
78 struct CacheStream : CachedFileStream {
79 AddBufferFn AddBuffer;
80 sys::fs::TempFile TempFile;
81 std::string ModuleName;
82 unsigned Task;
83
84 CacheStream(std::unique_ptr<raw_pwrite_stream> OS, AddBufferFn AddBuffer,
85 sys::fs::TempFile TempFile, std::string EntryPath,
86 std::string ModuleName, unsigned Task)
87 : CachedFileStream(std::move(OS), std::move(EntryPath)),
88 AddBuffer(std::move(AddBuffer)), TempFile(std::move(TempFile)),
89 ModuleName(ModuleName), Task(Task) {}
90
91 Error commit() override {
92 Error E = CachedFileStream::commit();
93 if (E)
94 return E;
95
96 // Make sure the stream is closed before committing it.
97 OS.reset();
98
99 // Open the file first to avoid racing with a cache pruner.
100 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
101 MemoryBuffer::getOpenFile(
102 FD: sys::fs::convertFDToNativeFile(FD: TempFile.FD), Filename: ObjectPathName,
103 /*FileSize=*/-1, /*RequiresNullTerminator=*/false);
104 if (!MBOrErr) {
105 std::error_code EC = MBOrErr.getError();
106 return createStringError(EC, S: Twine("Failed to open new cache file ") +
107 TempFile.TmpName + ": " +
108 EC.message() + "\n");
109 }
110
111 // On POSIX systems, this will atomically replace the destination if
112 // it already exists. We try to emulate this on Windows, but this may
113 // fail with a permission denied error (for example, if the destination
114 // is currently opened by another process that does not give us the
115 // sharing permissions we need). Since the existing file should be
116 // semantically equivalent to the one we are trying to write, we give
117 // AddBuffer a copy of the bytes we wrote in that case. We do this
118 // instead of just using the existing file, because the pruner might
119 // delete the file before we get a chance to use it.
120 E = TempFile.keep(Name: ObjectPathName);
121 E = handleErrors(E: std::move(E), Hs: [&](const ECError &E) -> Error {
122 std::error_code EC = E.convertToErrorCode();
123 if (EC != errc::permission_denied)
124 return createStringError(
125 EC, S: Twine("Failed to rename temporary file ") +
126 TempFile.TmpName + " to " + ObjectPathName + ": " +
127 EC.message() + "\n");
128
129 auto MBCopy = MemoryBuffer::getMemBufferCopy(InputData: (*MBOrErr)->getBuffer(),
130 BufferName: ObjectPathName);
131 MBOrErr = std::move(MBCopy);
132
133 // FIXME: should we consume the discard error?
134 consumeError(Err: TempFile.discard());
135
136 return Error::success();
137 });
138
139 if (E)
140 return E;
141
142 AddBuffer(Task, ModuleName, std::move(*MBOrErr));
143 return Error::success();
144 }
145 };
146
147 return [=](size_t Task, const Twine &ModuleName)
148 -> Expected<std::unique_ptr<CachedFileStream>> {
149 // Create the cache directory if not already done. Doing this lazily
150 // ensures the filesystem isn't mutated until the cache is.
151 if (std::error_code EC = sys::fs::create_directories(
152 path: CacheDirectoryPath, /*IgnoreExisting=*/true))
153 return createStringError(EC, S: Twine("can't create cache directory ") +
154 CacheDirectoryPath + ": " +
155 EC.message());
156
157 // Write to a temporary to avoid race condition
158 SmallString<64> TempFilenameModel;
159 sys::path::append(path&: TempFilenameModel, a: CacheDirectoryPath,
160 b: TempFilePrefix + "-%%%%%%.tmp.o");
161 Expected<sys::fs::TempFile> Temp = sys::fs::TempFile::create(
162 Model: TempFilenameModel, Mode: sys::fs::owner_read | sys::fs::owner_write);
163 if (!Temp)
164 return createStringError(EC: errc::io_error,
165 S: toString(E: Temp.takeError()) + ": " + CacheName +
166 ": Can't get a temporary file");
167
168 // This CacheStream will move the temporary file into the cache when done.
169 return std::make_unique<CacheStream>(
170 args: std::make_unique<raw_fd_ostream>(args&: Temp->FD, /* ShouldClose */ args: false),
171 args: AddBuffer, args: std::move(*Temp), args: std::string(EntryPath), args: ModuleName.str(),
172 args&: Task);
173 };
174 };
175 return FileCache(Func, CacheDirectoryPathRef.str());
176}
177