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 "llvm/Support/Windows/WindowsSupport.h"
25#include <io.h>
26#endif
27
28using namespace llvm;
29
30Expected<FileCache> llvm::localCache(const Twine &CacheNameRef,
31 const Twine &TempFilePrefixRef,
32 const Twine &CacheDirectoryPathRef,
33 AddBufferFn AddBuffer, bool CacheRename) {
34
35 // Create local copies which are safely captured-by-copy in lambdas
36 SmallString<64> CacheName, TempFilePrefix, CacheDirectoryPath;
37 CacheNameRef.toVector(Out&: CacheName);
38 TempFilePrefixRef.toVector(Out&: TempFilePrefix);
39 CacheDirectoryPathRef.toVector(Out&: CacheDirectoryPath);
40
41 auto Func = [=](unsigned Task, StringRef Key,
42 const Twine &ModuleName) -> Expected<AddStreamFn> {
43 // This choice of file name allows the cache to be pruned (see pruneCache()
44 // in include/llvm/Support/CachePruning.h).
45 SmallString<64> EntryPath;
46 sys::path::append(path&: EntryPath, a: CacheDirectoryPath, b: "llvmcache-" + Key);
47 // First, see if we have a cache hit.
48 SmallString<64> ResultPath;
49 Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForRead(
50 Name: Twine(EntryPath), Flags: sys::fs::OF_UpdateAtime, RealPath: &ResultPath);
51 std::error_code EC;
52 if (FDOrErr) {
53 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
54 MemoryBuffer::getOpenFile(FD: *FDOrErr, Filename: EntryPath,
55 /*FileSize=*/-1,
56 /*RequiresNullTerminator=*/false);
57 sys::fs::closeFile(F&: *FDOrErr);
58 if (MBOrErr) {
59 AddBuffer(Task, ModuleName, std::move(*MBOrErr));
60 return AddStreamFn();
61 }
62 EC = MBOrErr.getError();
63 } else {
64 EC = errorToErrorCode(Err: FDOrErr.takeError());
65 }
66
67 // On Windows we can fail to open a cache file with a permission denied
68 // error. This generally means that another process has requested to delete
69 // the file while it is still open, but it could also mean that another
70 // process has opened the file without the sharing permissions we need.
71 // Since the file is probably being deleted we handle it in the same way as
72 // if the file did not exist at all.
73 if (EC != errc::no_such_file_or_directory && EC != errc::permission_denied)
74 return createStringError(EC, S: Twine("Failed to open cache file ") +
75 EntryPath + ": " + EC.message() + "\n");
76
77 // This file stream is responsible for commiting the resulting file to the
78 // cache and calling AddBuffer to add it to the link.
79 struct CacheStream : CachedFileStream {
80 AddBufferFn AddBuffer;
81 sys::fs::TempFile TempFile;
82 std::string ModuleName;
83 unsigned Task;
84
85 CacheStream(std::unique_ptr<raw_pwrite_stream> OS, AddBufferFn AddBuffer,
86 sys::fs::TempFile TempFile, std::string EntryPath,
87 std::string ModuleName, unsigned Task)
88 : CachedFileStream(std::move(OS), std::move(EntryPath)),
89 AddBuffer(std::move(AddBuffer)), TempFile(std::move(TempFile)),
90 ModuleName(ModuleName), Task(Task) {}
91
92 Error commit() override {
93 Error E = CachedFileStream::commit();
94 if (E)
95 return E;
96
97 // Make sure the stream is closed before committing it.
98 OS.reset();
99
100 // Open the file first to avoid racing with a cache pruner.
101 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
102 MemoryBuffer::getOpenFile(
103 FD: sys::fs::convertFDToNativeFile(FD: TempFile.FD), Filename: ObjectPathName,
104 /*FileSize=*/-1, /*RequiresNullTerminator=*/false);
105 if (!MBOrErr) {
106 std::error_code EC = MBOrErr.getError();
107 return createStringError(EC, S: Twine("Failed to open new cache file ") +
108 TempFile.TmpName + ": " +
109 EC.message() + "\n");
110 }
111
112 // On POSIX systems, this will atomically replace the destination if
113 // it already exists. We try to emulate this on Windows, but this may
114 // fail with a permission denied error (for example, if the destination
115 // is currently opened by another process that does not give us the
116 // sharing permissions we need). Since the existing file should be
117 // semantically equivalent to the one we are trying to write, we give
118 // AddBuffer a copy of the bytes we wrote in that case. We do this
119 // instead of just using the existing file, because the pruner might
120 // delete the file before we get a chance to use it.
121 E = TempFile.keep(Name: ObjectPathName);
122 E = handleErrors(E: std::move(E), Hs: [&](const ECError &E) -> Error {
123 std::error_code EC = E.convertToErrorCode();
124 if (EC != errc::permission_denied)
125 return createStringError(
126 EC, S: Twine("Failed to rename temporary file ") +
127 TempFile.TmpName + " to " + ObjectPathName + ": " +
128 EC.message() + "\n");
129
130 auto MBCopy = MemoryBuffer::getMemBufferCopy(InputData: (*MBOrErr)->getBuffer(),
131 BufferName: ObjectPathName);
132 MBOrErr = std::move(MBCopy);
133
134 // FIXME: should we consume the discard error?
135 consumeError(Err: TempFile.discard());
136
137 return Error::success();
138 });
139
140 if (E)
141 return E;
142
143 AddBuffer(Task, ModuleName, std::move(*MBOrErr));
144 return Error::success();
145 }
146 };
147
148 // This class is responsible for renaming/moving existing file into a
149 // cache directory. The path for an input file is passed through a string
150 // stream.
151 struct MoveFileToCache : CachedFileStream {
152 AddBufferFn AddBuffer;
153 std::string ModuleName;
154 size_t Task;
155 StringRef FilePath;
156
157 MoveFileToCache(AddBufferFn AddBuffer, std::string EntryPath,
158 std::string ModuleID, size_t Task)
159 : CachedFileStream({}, std::move(EntryPath)),
160 AddBuffer(std::move(AddBuffer)), ModuleName(ModuleID), Task(Task) {}
161 virtual ~MoveFileToCache() = default;
162
163 virtual Error commit(std::unique_ptr<MemoryBuffer> MemBuf) override {
164 Error E = CachedFileStream::commit();
165 if (E)
166 return E;
167
168 FilePath = MemBuf->getBufferIdentifier();
169 assert(!FilePath.empty() && "File path is empty.");
170
171 // Rename/move native object file into cache directory, if they are
172 // located the same device/logical drive, otherwise we use a copy.
173 std::error_code EC = sys::fs::rename(from: FilePath, to: ObjectPathName);
174#ifdef _WIN32
175 if (EC ==
176 std::error_code(ERROR_NOT_SAME_DEVICE, std::system_category()))
177#else
178 if (EC == std::make_error_code(e: std::errc::cross_device_link))
179#endif
180 EC = sys::fs::copy_file(From: FilePath, To: ObjectPathName);
181 if (EC)
182 return createStringError(EC, S: Twine("Failed to rename or copy file ") +
183 FilePath + " to " + ObjectPathName +
184 ": " + EC.message() + "\n");
185
186 AddBuffer(Task, ModuleName, std::move(MemBuf));
187
188 return Error::success();
189 }
190 };
191
192 return [=](size_t Task, const Twine &ModuleName)
193 -> Expected<std::unique_ptr<CachedFileStream>> {
194 // Create the cache directory if not already done. Doing this lazily
195 // ensures the filesystem isn't mutated until the cache is.
196 if (std::error_code EC = sys::fs::create_directories(
197 path: CacheDirectoryPath, /*IgnoreExisting=*/true))
198 return createStringError(EC, S: Twine("can't create cache directory ") +
199 CacheDirectoryPath + ": " +
200 EC.message());
201 // MoveFileToChache class will rename/move the file into the cache on
202 // destruction.
203 if (CacheRename) {
204 return std::make_unique<MoveFileToCache>(
205 args: AddBuffer, args: std::string(EntryPath.str()), args: ModuleName.str(), args&: Task);
206 }
207
208 // Write to a temporary to avoid race condition
209 SmallString<64> TempFilenameModel;
210 sys::path::append(path&: TempFilenameModel, a: CacheDirectoryPath,
211 b: TempFilePrefix + "-%%%%%%.tmp.o");
212 Expected<sys::fs::TempFile> Temp = sys::fs::TempFile::create(
213 Model: TempFilenameModel, Mode: sys::fs::owner_read | sys::fs::owner_write);
214 if (!Temp)
215 return createStringError(EC: errc::io_error,
216 S: toString(E: Temp.takeError()) + ": " + CacheName +
217 ": Can't get a temporary file");
218
219 // This CacheStream will move the temporary file into the cache when done.
220 return std::make_unique<CacheStream>(
221 args: std::make_unique<raw_fd_ostream>(args&: Temp->FD, /* ShouldClose */ args: false),
222 args: AddBuffer, args: std::move(*Temp), args: std::string(EntryPath), args: ModuleName.str(),
223 args&: Task);
224 };
225 };
226 return FileCache(Func, CacheDirectoryPathRef.str());
227}
228