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>> 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 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 } 112 113 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: 140 RemoveUniqueLockFileOnSignal(StringRef Name) 141 : Filename(Name), RemoveImmediately(true) { 142 sys::RemoveFileOnSignal(Filename, nullptr); 143 } 144 145 ~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 } 154 155 void lockAcquired() { RemoveImmediately = false; } 156 }; 157 158 } // end anonymous namespace 159 160 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.str())); 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.str())); 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.str())); 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.str())); 252 setError(EC, S); 253 return; 254 } 255 } 256 } 257 258 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 } 267 268 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 } 279 280 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 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 } 347 348 std::error_code LockFileManager::unsafeRemoveLockFile() { 349 return sys::fs::remove(LockFileName); 350 } 351