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/None.h" 11 #include "llvm/ADT/SmallVector.h" 12 #include "llvm/ADT/StringExtras.h" 13 #include "llvm/Support/Errc.h" 14 #include "llvm/Support/ErrorOr.h" 15 #include "llvm/Support/FileSystem.h" 16 #include "llvm/Support/MemoryBuffer.h" 17 #include "llvm/Support/Process.h" 18 #include "llvm/Support/Signals.h" 19 #include "llvm/Support/raw_ostream.h" 20 #include <cerrno> 21 #include <chrono> 22 #include <ctime> 23 #include <memory> 24 #include <random> 25 #include <sys/stat.h> 26 #include <sys/types.h> 27 #include <system_error> 28 #include <thread> 29 #include <tuple> 30 31 #ifdef _WIN32 32 #include <windows.h> 33 #endif 34 #if LLVM_ON_UNIX 35 #include <unistd.h> 36 #endif 37 38 #if defined(__APPLE__) && defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) && (__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ > 1050) 39 #define USE_OSX_GETHOSTUUID 1 40 #else 41 #define USE_OSX_GETHOSTUUID 0 42 #endif 43 44 #if USE_OSX_GETHOSTUUID 45 #include <uuid/uuid.h> 46 #endif 47 48 using namespace llvm; 49 50 /// Attempt to read the lock file with the given name, if it exists. 51 /// 52 /// \param LockFileName The name of the lock file to read. 53 /// 54 /// \returns The process ID of the process that owns this lock file 55 Optional<std::pair<std::string, int> > 56 LockFileManager::readLockFile(StringRef LockFileName) { 57 // Read the owning host and PID out of the lock file. If it appears that the 58 // owning process is dead, the lock file is invalid. 59 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr = 60 MemoryBuffer::getFile(LockFileName); 61 if (!MBOrErr) { 62 sys::fs::remove(LockFileName); 63 return None; 64 } 65 MemoryBuffer &MB = *MBOrErr.get(); 66 67 StringRef Hostname; 68 StringRef PIDStr; 69 std::tie(Hostname, PIDStr) = getToken(MB.getBuffer(), " "); 70 PIDStr = PIDStr.substr(PIDStr.find_first_not_of(" ")); 71 int PID; 72 if (!PIDStr.getAsInteger(10, PID)) { 73 auto Owner = std::make_pair(std::string(Hostname), PID); 74 if (processStillExecuting(Owner.first, Owner.second)) 75 return Owner; 76 } 77 78 // Delete the lock file. It's invalid anyway. 79 sys::fs::remove(LockFileName); 80 return None; 81 } 82 83 static std::error_code getHostID(SmallVectorImpl<char> &HostID) { 84 HostID.clear(); 85 86 #if USE_OSX_GETHOSTUUID 87 // On OS X, use the more stable hardware UUID instead of hostname. 88 struct timespec wait = {1, 0}; // 1 second. 89 uuid_t uuid; 90 if (gethostuuid(uuid, &wait) != 0) 91 return std::error_code(errno, std::system_category()); 92 93 uuid_string_t UUIDStr; 94 uuid_unparse(uuid, UUIDStr); 95 StringRef UUIDRef(UUIDStr); 96 HostID.append(UUIDRef.begin(), UUIDRef.end()); 97 98 #elif LLVM_ON_UNIX 99 char HostName[256]; 100 HostName[255] = 0; 101 HostName[0] = 0; 102 gethostname(HostName, 255); 103 StringRef HostNameRef(HostName); 104 HostID.append(HostNameRef.begin(), HostNameRef.end()); 105 106 #else 107 StringRef Dummy("localhost"); 108 HostID.append(Dummy.begin(), Dummy.end()); 109 #endif 110 111 return std::error_code(); 112 } 113 114 bool LockFileManager::processStillExecuting(StringRef HostID, int PID) { 115 #if LLVM_ON_UNIX && !defined(__ANDROID__) 116 SmallString<256> StoredHostID; 117 if (getHostID(StoredHostID)) 118 return true; // Conservatively assume it's executing on error. 119 120 // Check whether the process is dead. If so, we're done. 121 if (StoredHostID == HostID && getsid(PID) == -1 && errno == ESRCH) 122 return false; 123 #endif 124 125 return true; 126 } 127 128 namespace { 129 130 /// An RAII helper object ensure that the unique lock file is removed. 131 /// 132 /// Ensures that if there is an error or a signal before we finish acquiring the 133 /// lock, the unique file will be removed. And if we successfully take the lock, 134 /// the signal handler is left in place so that signals while the lock is held 135 /// will remove the unique lock file. The caller should ensure there is a 136 /// matching call to sys::DontRemoveFileOnSignal when the lock is released. 137 class RemoveUniqueLockFileOnSignal { 138 StringRef Filename; 139 bool RemoveImmediately; 140 public: 141 RemoveUniqueLockFileOnSignal(StringRef Name) 142 : Filename(Name), RemoveImmediately(true) { 143 sys::RemoveFileOnSignal(Filename, nullptr); 144 } 145 146 ~RemoveUniqueLockFileOnSignal() { 147 if (!RemoveImmediately) { 148 // Leave the signal handler enabled. It will be removed when the lock is 149 // released. 150 return; 151 } 152 sys::fs::remove(Filename); 153 sys::DontRemoveFileOnSignal(Filename); 154 } 155 156 void lockAcquired() { RemoveImmediately = false; } 157 }; 158 159 } // end anonymous namespace 160 161 LockFileManager::LockFileManager(StringRef FileName) 162 { 163 this->FileName = FileName; 164 if (std::error_code EC = sys::fs::make_absolute(this->FileName)) { 165 std::string S("failed to obtain absolute path for "); 166 S.append(std::string(this->FileName.str())); 167 setError(EC, S); 168 return; 169 } 170 LockFileName = this->FileName; 171 LockFileName += ".lock"; 172 173 // If the lock file already exists, don't bother to try to create our own 174 // lock file; it won't work anyway. Just figure out who owns this lock file. 175 if ((Owner = readLockFile(LockFileName))) 176 return; 177 178 // Create a lock file that is unique to this instance. 179 UniqueLockFileName = LockFileName; 180 UniqueLockFileName += "-%%%%%%%%"; 181 int UniqueLockFileID; 182 if (std::error_code EC = sys::fs::createUniqueFile( 183 UniqueLockFileName, UniqueLockFileID, UniqueLockFileName)) { 184 std::string S("failed to create unique file "); 185 S.append(std::string(UniqueLockFileName.str())); 186 setError(EC, S); 187 return; 188 } 189 190 // Write our process ID to our unique lock file. 191 { 192 SmallString<256> HostID; 193 if (auto EC = getHostID(HostID)) { 194 setError(EC, "failed to get host id"); 195 return; 196 } 197 198 raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true); 199 Out << HostID << ' ' << sys::Process::getProcessId(); 200 Out.close(); 201 202 if (Out.has_error()) { 203 // We failed to write out PID, so report the error, remove the 204 // unique lock file, and fail. 205 std::string S("failed to write to "); 206 S.append(std::string(UniqueLockFileName.str())); 207 setError(Out.error(), S); 208 sys::fs::remove(UniqueLockFileName); 209 return; 210 } 211 } 212 213 // Clean up the unique file on signal, which also releases the lock if it is 214 // held since the .lock symlink will point to a nonexistent file. 215 RemoveUniqueLockFileOnSignal RemoveUniqueFile(UniqueLockFileName); 216 217 while (true) { 218 // Create a link from the lock file name. If this succeeds, we're done. 219 std::error_code EC = 220 sys::fs::create_link(UniqueLockFileName, LockFileName); 221 if (!EC) { 222 RemoveUniqueFile.lockAcquired(); 223 return; 224 } 225 226 if (EC != errc::file_exists) { 227 std::string S("failed to create link "); 228 raw_string_ostream OSS(S); 229 OSS << LockFileName.str() << " to " << UniqueLockFileName.str(); 230 setError(EC, OSS.str()); 231 return; 232 } 233 234 // Someone else managed to create the lock file first. Read the process ID 235 // from the lock file. 236 if ((Owner = readLockFile(LockFileName))) { 237 // Wipe out our unique lock file (it's useless now) 238 sys::fs::remove(UniqueLockFileName); 239 return; 240 } 241 242 if (!sys::fs::exists(LockFileName)) { 243 // The previous owner released the lock file before we could read it. 244 // Try to get ownership again. 245 continue; 246 } 247 248 // There is a lock file that nobody owns; try to clean it up and get 249 // ownership. 250 if ((EC = sys::fs::remove(LockFileName))) { 251 std::string S("failed to remove lockfile "); 252 S.append(std::string(UniqueLockFileName.str())); 253 setError(EC, S); 254 return; 255 } 256 } 257 } 258 259 LockFileManager::LockFileState LockFileManager::getState() const { 260 if (Owner) 261 return LFS_Shared; 262 263 if (ErrorCode) 264 return LFS_Error; 265 266 return LFS_Owned; 267 } 268 269 std::string LockFileManager::getErrorMessage() const { 270 if (ErrorCode) { 271 std::string Str(ErrorDiagMsg); 272 std::string ErrCodeMsg = ErrorCode.message(); 273 raw_string_ostream OSS(Str); 274 if (!ErrCodeMsg.empty()) 275 OSS << ": " << ErrCodeMsg; 276 return OSS.str(); 277 } 278 return ""; 279 } 280 281 LockFileManager::~LockFileManager() { 282 if (getState() != LFS_Owned) 283 return; 284 285 // Since we own the lock, remove the lock file and our own unique lock file. 286 sys::fs::remove(LockFileName); 287 sys::fs::remove(UniqueLockFileName); 288 // The unique file is now gone, so remove it from the signal handler. This 289 // matches a sys::RemoveFileOnSignal() in LockFileManager(). 290 sys::DontRemoveFileOnSignal(UniqueLockFileName); 291 } 292 293 LockFileManager::WaitForUnlockResult 294 LockFileManager::waitForUnlock(const unsigned MaxSeconds) { 295 if (getState() != LFS_Shared) 296 return Res_Success; 297 298 // Since we don't yet have an event-based method to wait for the lock file, 299 // implement randomized exponential backoff, similar to Ethernet collision 300 // algorithm. This improves performance on machines with high core counts 301 // when the file lock is heavily contended by multiple clang processes 302 const unsigned long MinWaitDurationMS = 10; 303 const unsigned long MaxWaitMultiplier = 50; // 500ms max wait 304 unsigned long WaitMultiplier = 1; 305 unsigned long ElapsedTimeSeconds = 0; 306 307 std::random_device Device; 308 std::default_random_engine Engine(Device()); 309 310 auto StartTime = std::chrono::steady_clock::now(); 311 312 do { 313 // FIXME: implement event-based waiting 314 315 // Sleep for the designated interval, to allow the owning process time to 316 // finish up and remove the lock file. 317 std::uniform_int_distribution<unsigned long> Distribution(1, 318 WaitMultiplier); 319 unsigned long WaitDurationMS = MinWaitDurationMS * Distribution(Engine); 320 std::this_thread::sleep_for(std::chrono::milliseconds(WaitDurationMS)); 321 322 if (sys::fs::access(LockFileName.c_str(), sys::fs::AccessMode::Exist) == 323 errc::no_such_file_or_directory) { 324 // If the original file wasn't created, somone thought the lock was dead. 325 if (!sys::fs::exists(FileName)) 326 return Res_OwnerDied; 327 return Res_Success; 328 } 329 330 // If the process owning the lock died without cleaning up, just bail out. 331 if (!processStillExecuting((*Owner).first, (*Owner).second)) 332 return Res_OwnerDied; 333 334 WaitMultiplier *= 2; 335 if (WaitMultiplier > MaxWaitMultiplier) { 336 WaitMultiplier = MaxWaitMultiplier; 337 } 338 339 ElapsedTimeSeconds = std::chrono::duration_cast<std::chrono::seconds>( 340 std::chrono::steady_clock::now() - StartTime) 341 .count(); 342 343 } while (ElapsedTimeSeconds < MaxSeconds); 344 345 // Give up. 346 return Res_Timeout; 347 } 348 349 std::error_code LockFileManager::unsafeRemoveLockFile() { 350 return sys::fs::remove(LockFileName); 351 } 352