1 //===--- LockFileManager.cpp - File-level Locking Utility------------------===//
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 #include "llvm/Support/LockFileManager.h"
10 #include "llvm/ADT/SmallVector.h"
11 #include "llvm/ADT/StringExtras.h"
12 #include "llvm/Support/Errc.h"
13 #include "llvm/Support/ErrorOr.h"
14 #include "llvm/Support/FileSystem.h"
15 #include "llvm/Support/MemoryBuffer.h"
16 #include "llvm/Support/Process.h"
17 #include "llvm/Support/Signals.h"
18 #include "llvm/Support/raw_ostream.h"
19 #include <cerrno>
20 #include <chrono>
21 #include <ctime>
22 #include <memory>
23 #include <random>
24 #include <sys/stat.h>
25 #include <sys/types.h>
26 #include <system_error>
27 #include <thread>
28 #include <tuple>
29
30 #ifdef _WIN32
31 #include <windows.h>
32 #endif
33 #if LLVM_ON_UNIX
34 #include <unistd.h>
35 #endif
36
37 #if defined(__APPLE__) && defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) && (__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ > 1050)
38 #define USE_OSX_GETHOSTUUID 1
39 #else
40 #define USE_OSX_GETHOSTUUID 0
41 #endif
42
43 #if USE_OSX_GETHOSTUUID
44 #include <uuid/uuid.h>
45 #endif
46
47 using namespace llvm;
48
49 /// Attempt to read the lock file with the given name, if it exists.
50 ///
51 /// \param LockFileName The name of the lock file to read.
52 ///
53 /// \returns The process ID of the process that owns this lock file
54 std::optional<std::pair<std::string, int>>
readLockFile(StringRef LockFileName)55 LockFileManager::readLockFile(StringRef LockFileName) {
56 // Read the owning host and PID out of the lock file. If it appears that the
57 // owning process is dead, the lock file is invalid.
58 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
59 MemoryBuffer::getFile(LockFileName);
60 if (!MBOrErr) {
61 sys::fs::remove(LockFileName);
62 return std::nullopt;
63 }
64 MemoryBuffer &MB = *MBOrErr.get();
65
66 StringRef Hostname;
67 StringRef PIDStr;
68 std::tie(Hostname, PIDStr) = getToken(MB.getBuffer(), " ");
69 PIDStr = PIDStr.substr(PIDStr.find_first_not_of(" "));
70 int PID;
71 if (!PIDStr.getAsInteger(10, PID)) {
72 auto Owner = std::make_pair(std::string(Hostname), PID);
73 if (processStillExecuting(Owner.first, Owner.second))
74 return Owner;
75 }
76
77 // Delete the lock file. It's invalid anyway.
78 sys::fs::remove(LockFileName);
79 return std::nullopt;
80 }
81
getHostID(SmallVectorImpl<char> & HostID)82 static std::error_code getHostID(SmallVectorImpl<char> &HostID) {
83 HostID.clear();
84
85 #if USE_OSX_GETHOSTUUID
86 // On OS X, use the more stable hardware UUID instead of hostname.
87 struct timespec wait = {1, 0}; // 1 second.
88 uuid_t uuid;
89 if (gethostuuid(uuid, &wait) != 0)
90 return std::error_code(errno, std::system_category());
91
92 uuid_string_t UUIDStr;
93 uuid_unparse(uuid, UUIDStr);
94 StringRef UUIDRef(UUIDStr);
95 HostID.append(UUIDRef.begin(), UUIDRef.end());
96
97 #elif LLVM_ON_UNIX
98 char HostName[256];
99 HostName[255] = 0;
100 HostName[0] = 0;
101 gethostname(HostName, 255);
102 StringRef HostNameRef(HostName);
103 HostID.append(HostNameRef.begin(), HostNameRef.end());
104
105 #else
106 StringRef Dummy("localhost");
107 HostID.append(Dummy.begin(), Dummy.end());
108 #endif
109
110 return std::error_code();
111 }
112
processStillExecuting(StringRef HostID,int PID)113 bool LockFileManager::processStillExecuting(StringRef HostID, int PID) {
114 #if LLVM_ON_UNIX && !defined(__ANDROID__)
115 SmallString<256> StoredHostID;
116 if (getHostID(StoredHostID))
117 return true; // Conservatively assume it's executing on error.
118
119 // Check whether the process is dead. If so, we're done.
120 if (StoredHostID == HostID && getsid(PID) == -1 && errno == ESRCH)
121 return false;
122 #endif
123
124 return true;
125 }
126
127 namespace {
128
129 /// An RAII helper object ensure that the unique lock file is removed.
130 ///
131 /// Ensures that if there is an error or a signal before we finish acquiring the
132 /// lock, the unique file will be removed. And if we successfully take the lock,
133 /// the signal handler is left in place so that signals while the lock is held
134 /// will remove the unique lock file. The caller should ensure there is a
135 /// matching call to sys::DontRemoveFileOnSignal when the lock is released.
136 class RemoveUniqueLockFileOnSignal {
137 StringRef Filename;
138 bool RemoveImmediately;
139 public:
RemoveUniqueLockFileOnSignal(StringRef Name)140 RemoveUniqueLockFileOnSignal(StringRef Name)
141 : Filename(Name), RemoveImmediately(true) {
142 sys::RemoveFileOnSignal(Filename, nullptr);
143 }
144
~RemoveUniqueLockFileOnSignal()145 ~RemoveUniqueLockFileOnSignal() {
146 if (!RemoveImmediately) {
147 // Leave the signal handler enabled. It will be removed when the lock is
148 // released.
149 return;
150 }
151 sys::fs::remove(Filename);
152 sys::DontRemoveFileOnSignal(Filename);
153 }
154
lockAcquired()155 void lockAcquired() { RemoveImmediately = false; }
156 };
157
158 } // end anonymous namespace
159
LockFileManager(StringRef FileName)160 LockFileManager::LockFileManager(StringRef FileName)
161 {
162 this->FileName = FileName;
163 if (std::error_code EC = sys::fs::make_absolute(this->FileName)) {
164 std::string S("failed to obtain absolute path for ");
165 S.append(std::string(this->FileName));
166 setError(EC, S);
167 return;
168 }
169 LockFileName = this->FileName;
170 LockFileName += ".lock";
171
172 // If the lock file already exists, don't bother to try to create our own
173 // lock file; it won't work anyway. Just figure out who owns this lock file.
174 if ((Owner = readLockFile(LockFileName)))
175 return;
176
177 // Create a lock file that is unique to this instance.
178 UniqueLockFileName = LockFileName;
179 UniqueLockFileName += "-%%%%%%%%";
180 int UniqueLockFileID;
181 if (std::error_code EC = sys::fs::createUniqueFile(
182 UniqueLockFileName, UniqueLockFileID, UniqueLockFileName)) {
183 std::string S("failed to create unique file ");
184 S.append(std::string(UniqueLockFileName));
185 setError(EC, S);
186 return;
187 }
188
189 // Write our process ID to our unique lock file.
190 {
191 SmallString<256> HostID;
192 if (auto EC = getHostID(HostID)) {
193 setError(EC, "failed to get host id");
194 return;
195 }
196
197 raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
198 Out << HostID << ' ' << sys::Process::getProcessId();
199 Out.close();
200
201 if (Out.has_error()) {
202 // We failed to write out PID, so report the error, remove the
203 // unique lock file, and fail.
204 std::string S("failed to write to ");
205 S.append(std::string(UniqueLockFileName));
206 setError(Out.error(), S);
207 sys::fs::remove(UniqueLockFileName);
208 return;
209 }
210 }
211
212 // Clean up the unique file on signal, which also releases the lock if it is
213 // held since the .lock symlink will point to a nonexistent file.
214 RemoveUniqueLockFileOnSignal RemoveUniqueFile(UniqueLockFileName);
215
216 while (true) {
217 // Create a link from the lock file name. If this succeeds, we're done.
218 std::error_code EC =
219 sys::fs::create_link(UniqueLockFileName, LockFileName);
220 if (!EC) {
221 RemoveUniqueFile.lockAcquired();
222 return;
223 }
224
225 if (EC != errc::file_exists) {
226 std::string S("failed to create link ");
227 raw_string_ostream OSS(S);
228 OSS << LockFileName.str() << " to " << UniqueLockFileName.str();
229 setError(EC, OSS.str());
230 return;
231 }
232
233 // Someone else managed to create the lock file first. Read the process ID
234 // from the lock file.
235 if ((Owner = readLockFile(LockFileName))) {
236 // Wipe out our unique lock file (it's useless now)
237 sys::fs::remove(UniqueLockFileName);
238 return;
239 }
240
241 if (!sys::fs::exists(LockFileName)) {
242 // The previous owner released the lock file before we could read it.
243 // Try to get ownership again.
244 continue;
245 }
246
247 // There is a lock file that nobody owns; try to clean it up and get
248 // ownership.
249 if ((EC = sys::fs::remove(LockFileName))) {
250 std::string S("failed to remove lockfile ");
251 S.append(std::string(UniqueLockFileName));
252 setError(EC, S);
253 return;
254 }
255 }
256 }
257
getState() const258 LockFileManager::LockFileState LockFileManager::getState() const {
259 if (Owner)
260 return LFS_Shared;
261
262 if (ErrorCode)
263 return LFS_Error;
264
265 return LFS_Owned;
266 }
267
getErrorMessage() const268 std::string LockFileManager::getErrorMessage() const {
269 if (ErrorCode) {
270 std::string Str(ErrorDiagMsg);
271 std::string ErrCodeMsg = ErrorCode.message();
272 raw_string_ostream OSS(Str);
273 if (!ErrCodeMsg.empty())
274 OSS << ": " << ErrCodeMsg;
275 return OSS.str();
276 }
277 return "";
278 }
279
~LockFileManager()280 LockFileManager::~LockFileManager() {
281 if (getState() != LFS_Owned)
282 return;
283
284 // Since we own the lock, remove the lock file and our own unique lock file.
285 sys::fs::remove(LockFileName);
286 sys::fs::remove(UniqueLockFileName);
287 // The unique file is now gone, so remove it from the signal handler. This
288 // matches a sys::RemoveFileOnSignal() in LockFileManager().
289 sys::DontRemoveFileOnSignal(UniqueLockFileName);
290 }
291
292 LockFileManager::WaitForUnlockResult
waitForUnlock(const unsigned MaxSeconds)293 LockFileManager::waitForUnlock(const unsigned MaxSeconds) {
294 if (getState() != LFS_Shared)
295 return Res_Success;
296
297 // Since we don't yet have an event-based method to wait for the lock file,
298 // implement randomized exponential backoff, similar to Ethernet collision
299 // algorithm. This improves performance on machines with high core counts
300 // when the file lock is heavily contended by multiple clang processes
301 const unsigned long MinWaitDurationMS = 10;
302 const unsigned long MaxWaitMultiplier = 50; // 500ms max wait
303 unsigned long WaitMultiplier = 1;
304 unsigned long ElapsedTimeSeconds = 0;
305
306 std::random_device Device;
307 std::default_random_engine Engine(Device());
308
309 auto StartTime = std::chrono::steady_clock::now();
310
311 do {
312 // FIXME: implement event-based waiting
313
314 // Sleep for the designated interval, to allow the owning process time to
315 // finish up and remove the lock file.
316 std::uniform_int_distribution<unsigned long> Distribution(1,
317 WaitMultiplier);
318 unsigned long WaitDurationMS = MinWaitDurationMS * Distribution(Engine);
319 std::this_thread::sleep_for(std::chrono::milliseconds(WaitDurationMS));
320
321 if (sys::fs::access(LockFileName.c_str(), sys::fs::AccessMode::Exist) ==
322 errc::no_such_file_or_directory) {
323 // If the original file wasn't created, somone thought the lock was dead.
324 if (!sys::fs::exists(FileName))
325 return Res_OwnerDied;
326 return Res_Success;
327 }
328
329 // If the process owning the lock died without cleaning up, just bail out.
330 if (!processStillExecuting((*Owner).first, (*Owner).second))
331 return Res_OwnerDied;
332
333 WaitMultiplier *= 2;
334 if (WaitMultiplier > MaxWaitMultiplier) {
335 WaitMultiplier = MaxWaitMultiplier;
336 }
337
338 ElapsedTimeSeconds = std::chrono::duration_cast<std::chrono::seconds>(
339 std::chrono::steady_clock::now() - StartTime)
340 .count();
341
342 } while (ElapsedTimeSeconds < MaxSeconds);
343
344 // Give up.
345 return Res_Timeout;
346 }
347
unsafeRemoveLockFile()348 std::error_code LockFileManager::unsafeRemoveLockFile() {
349 return sys::fs::remove(LockFileName);
350 }
351