1 //===--- LockFileManager.cpp - File-level Locking Utility------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 #include "llvm/Support/LockFileManager.h" 10 #include "llvm/ADT/STLExtras.h" 11 #include "llvm/ADT/StringExtras.h" 12 #include "llvm/Support/FileSystem.h" 13 #include "llvm/Support/MemoryBuffer.h" 14 #include "llvm/Support/raw_ostream.h" 15 #include <sys/stat.h> 16 #include <sys/types.h> 17 #if LLVM_ON_WIN32 18 #include <windows.h> 19 #endif 20 #if LLVM_ON_UNIX 21 #include <unistd.h> 22 #endif 23 using namespace llvm; 24 25 /// \brief Attempt to read the lock file with the given name, if it exists. 26 /// 27 /// \param LockFileName The name of the lock file to read. 28 /// 29 /// \returns The process ID of the process that owns this lock file 30 Optional<std::pair<std::string, int> > 31 LockFileManager::readLockFile(StringRef LockFileName) { 32 // Check whether the lock file exists. If not, clearly there's nothing 33 // to read, so we just return. 34 if (!sys::fs::exists(LockFileName)) 35 return None; 36 37 // Read the owning host and PID out of the lock file. If it appears that the 38 // owning process is dead, the lock file is invalid. 39 std::unique_ptr<MemoryBuffer> MB; 40 if (MemoryBuffer::getFile(LockFileName, MB)) 41 return None; 42 43 StringRef Hostname; 44 StringRef PIDStr; 45 std::tie(Hostname, PIDStr) = getToken(MB->getBuffer(), " "); 46 PIDStr = PIDStr.substr(PIDStr.find_first_not_of(" ")); 47 int PID; 48 if (!PIDStr.getAsInteger(10, PID)) 49 return std::make_pair(std::string(Hostname), PID); 50 51 // Delete the lock file. It's invalid anyway. 52 sys::fs::remove(LockFileName); 53 return None; 54 } 55 56 bool LockFileManager::processStillExecuting(StringRef Hostname, int PID) { 57 #if LLVM_ON_UNIX && !defined(__ANDROID__) 58 char MyHostname[256]; 59 MyHostname[255] = 0; 60 MyHostname[0] = 0; 61 gethostname(MyHostname, 255); 62 // Check whether the process is dead. If so, we're done. 63 if (MyHostname == Hostname && getsid(PID) == -1 && errno == ESRCH) 64 return false; 65 #endif 66 67 return true; 68 } 69 70 LockFileManager::LockFileManager(StringRef FileName) 71 { 72 this->FileName = FileName; 73 LockFileName = FileName; 74 LockFileName += ".lock"; 75 76 // If the lock file already exists, don't bother to try to create our own 77 // lock file; it won't work anyway. Just figure out who owns this lock file. 78 if ((Owner = readLockFile(LockFileName))) 79 return; 80 81 // Create a lock file that is unique to this instance. 82 UniqueLockFileName = LockFileName; 83 UniqueLockFileName += "-%%%%%%%%"; 84 int UniqueLockFileID; 85 if (error_code EC 86 = sys::fs::createUniqueFile(UniqueLockFileName.str(), 87 UniqueLockFileID, 88 UniqueLockFileName)) { 89 Error = EC; 90 return; 91 } 92 93 // Write our process ID to our unique lock file. 94 { 95 raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true); 96 97 #if LLVM_ON_UNIX 98 // FIXME: move getpid() call into LLVM 99 char hostname[256]; 100 hostname[255] = 0; 101 hostname[0] = 0; 102 gethostname(hostname, 255); 103 Out << hostname << ' ' << getpid(); 104 #else 105 Out << "localhost 1"; 106 #endif 107 Out.close(); 108 109 if (Out.has_error()) { 110 // We failed to write out PID, so make up an excuse, remove the 111 // unique lock file, and fail. 112 Error = make_error_code(errc::no_space_on_device); 113 sys::fs::remove(UniqueLockFileName.c_str()); 114 return; 115 } 116 } 117 118 while (1) { 119 // Create a symbolic link from the lock file name. If this succeeds, we're 120 // done. Note that we are using symbolic link because hard links are not 121 // supported by all filesystems. 122 error_code EC 123 = sys::fs::create_symbolic_link(UniqueLockFileName.str(), 124 LockFileName.str()); 125 if (EC == errc::success) 126 return; 127 128 if (EC != errc::file_exists) { 129 Error = EC; 130 return; 131 } 132 133 // Someone else managed to create the lock file first. Read the process ID 134 // from the lock file. 135 if ((Owner = readLockFile(LockFileName))) { 136 // Wipe out our unique lock file (it's useless now) 137 sys::fs::remove(UniqueLockFileName.str()); 138 return; 139 } 140 141 if (!sys::fs::exists(LockFileName.str())) { 142 // The previous owner released the lock file before we could read it. 143 // Try to get ownership again. 144 continue; 145 } 146 147 // There is a lock file that nobody owns; try to clean it up and get 148 // ownership. 149 if ((EC = sys::fs::remove(LockFileName.str()))) { 150 Error = EC; 151 return; 152 } 153 } 154 } 155 156 LockFileManager::LockFileState LockFileManager::getState() const { 157 if (Owner) 158 return LFS_Shared; 159 160 if (Error) 161 return LFS_Error; 162 163 return LFS_Owned; 164 } 165 166 LockFileManager::~LockFileManager() { 167 if (getState() != LFS_Owned) 168 return; 169 170 // Since we own the lock, remove the lock file and our own unique lock file. 171 sys::fs::remove(LockFileName.str()); 172 sys::fs::remove(UniqueLockFileName.str()); 173 } 174 175 void LockFileManager::waitForUnlock() { 176 if (getState() != LFS_Shared) 177 return; 178 179 #if LLVM_ON_WIN32 180 unsigned long Interval = 1; 181 #else 182 struct timespec Interval; 183 Interval.tv_sec = 0; 184 Interval.tv_nsec = 1000000; 185 #endif 186 // Don't wait more than five minutes for the file to appear. 187 unsigned MaxSeconds = 300; 188 bool LockFileGone = false; 189 do { 190 // Sleep for the designated interval, to allow the owning process time to 191 // finish up and remove the lock file. 192 // FIXME: Should we hook in to system APIs to get a notification when the 193 // lock file is deleted? 194 #if LLVM_ON_WIN32 195 Sleep(Interval); 196 #else 197 nanosleep(&Interval, NULL); 198 #endif 199 bool LockFileJustDisappeared = false; 200 201 // If the lock file is still expected to be there, check whether it still 202 // is. 203 if (!LockFileGone) { 204 bool Exists; 205 if (!sys::fs::exists(LockFileName.str(), Exists) && !Exists) { 206 LockFileGone = true; 207 LockFileJustDisappeared = true; 208 } 209 } 210 211 // If the lock file is no longer there, check if the original file is 212 // available now. 213 if (LockFileGone) { 214 if (sys::fs::exists(FileName.str())) { 215 return; 216 } 217 218 // The lock file is gone, so now we're waiting for the original file to 219 // show up. If this just happened, reset our waiting intervals and keep 220 // waiting. 221 if (LockFileJustDisappeared) { 222 MaxSeconds = 5; 223 224 #if LLVM_ON_WIN32 225 Interval = 1; 226 #else 227 Interval.tv_sec = 0; 228 Interval.tv_nsec = 1000000; 229 #endif 230 continue; 231 } 232 } 233 234 // If we're looking for the lock file to disappear, but the process 235 // owning the lock died without cleaning up, just bail out. 236 if (!LockFileGone && 237 !processStillExecuting((*Owner).first, (*Owner).second)) { 238 return; 239 } 240 241 // Exponentially increase the time we wait for the lock to be removed. 242 #if LLVM_ON_WIN32 243 Interval *= 2; 244 #else 245 Interval.tv_sec *= 2; 246 Interval.tv_nsec *= 2; 247 if (Interval.tv_nsec >= 1000000000) { 248 ++Interval.tv_sec; 249 Interval.tv_nsec -= 1000000000; 250 } 251 #endif 252 } while ( 253 #if LLVM_ON_WIN32 254 Interval < MaxSeconds * 1000 255 #else 256 Interval.tv_sec < (time_t)MaxSeconds 257 #endif 258 ); 259 260 // Give up. 261 } 262