lib/Support/LockFileManager.cpp

   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/Signals.h"
  18 #include "llvm/Support/raw_ostream.h"
  19 #include <cerrno>
  20 #include <ctime>
  21 #include <memory>
  22 #include <sys/stat.h>
  23 #include <sys/types.h>
  24 #include <system_error>
  25 #include <tuple>
  26 #ifdef _WIN32
  27 #include <windows.h>
  28 #endif
  29 #if LLVM_ON_UNIX
  30 #include <unistd.h>
  31 #endif
  32
  33 #if defined(__APPLE__) && defined(__MAC_OS_X_VERSION_MIN_REQUIRED) && (__MAC_OS_X_VERSION_MIN_REQUIRED > 1050)
  34 #define USE_OSX_GETHOSTUUID 1
  35 #else
  36 #define USE_OSX_GETHOSTUUID 0
  37 #endif
  38
  39 #if USE_OSX_GETHOSTUUID
  40 #include <uuid/uuid.h>
  41 #endif
  42
  43 using namespace llvm;
  44
  45 /// Attempt to read the lock file with the given name, if it exists.
  46 ///
  47 /// \param LockFileName The name of the lock file to read.
  48 ///
  49 /// \returns The process ID of the process that owns this lock file
  50 Optional<std::pair<std::string, int> >
  51 LockFileManager::readLockFile(StringRef LockFileName) {
  52   // Read the owning host and PID out of the lock file. If it appears that the
  53   // owning process is dead, the lock file is invalid.
  54   ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
  55       MemoryBuffer::getFile(LockFileName);
  56   if (!MBOrErr) {
  57     sys::fs::remove(LockFileName);
  58     return None;
  59   }
  60   MemoryBuffer &MB = *MBOrErr.get();
  61
  62   StringRef Hostname;
  63   StringRef PIDStr;
  64   std::tie(Hostname, PIDStr) = getToken(MB.getBuffer(), " ");
  65   PIDStr = PIDStr.substr(PIDStr.find_first_not_of(" "));
  66   int PID;
  67   if (!PIDStr.getAsInteger(10, PID)) {
  68     auto Owner = std::make_pair(std::string(Hostname), PID);
  69     if (processStillExecuting(Owner.first, Owner.second))
  70       return Owner;
  71   }
  72
  73   // Delete the lock file. It's invalid anyway.
  74   sys::fs::remove(LockFileName);
  75   return None;
  76 }
  77
  78 static std::error_code getHostID(SmallVectorImpl<char> &HostID) {
  79   HostID.clear();
  80
  81 #if USE_OSX_GETHOSTUUID
  82   // On OS X, use the more stable hardware UUID instead of hostname.
  83   struct timespec wait = {1, 0}; // 1 second.
  84   uuid_t uuid;
  85   if (gethostuuid(uuid, &wait) != 0)
  86     return std::error_code(errno, std::system_category());
  87
  88   uuid_string_t UUIDStr;
  89   uuid_unparse(uuid, UUIDStr);
  90   StringRef UUIDRef(UUIDStr);
  91   HostID.append(UUIDRef.begin(), UUIDRef.end());
  92
  93 #elif LLVM_ON_UNIX
  94   char HostName[256];
  95   HostName[255] = 0;
  96   HostName[0] = 0;
  97   gethostname(HostName, 255);
  98   StringRef HostNameRef(HostName);
  99   HostID.append(HostNameRef.begin(), HostNameRef.end());
 100
 101 #else
 102   StringRef Dummy("localhost");
 103   HostID.append(Dummy.begin(), Dummy.end());
 104 #endif
 105
 106   return std::error_code();
 107 }
 108
 109 bool LockFileManager::processStillExecuting(StringRef HostID, int PID) {
 110 #if LLVM_ON_UNIX && !defined(__ANDROID__)
 111   SmallString<256> StoredHostID;
 112   if (getHostID(StoredHostID))
 113     return true; // Conservatively assume it's executing on error.
 114
 115   // Check whether the process is dead. If so, we're done.
 116   if (StoredHostID == HostID && getsid(PID) == -1 && errno == ESRCH)
 117     return false;
 118 #endif
 119
 120   return true;
 121 }
 122
 123 namespace {
 124
 125 /// An RAII helper object ensure that the unique lock file is removed.
 126 ///
 127 /// Ensures that if there is an error or a signal before we finish acquiring the
 128 /// lock, the unique file will be removed. And if we successfully take the lock,
 129 /// the signal handler is left in place so that signals while the lock is held
 130 /// will remove the unique lock file. The caller should ensure there is a
 131 /// matching call to sys::DontRemoveFileOnSignal when the lock is released.
 132 class RemoveUniqueLockFileOnSignal {
 133   StringRef Filename;
 134   bool RemoveImmediately;
 135 public:
 136   RemoveUniqueLockFileOnSignal(StringRef Name)
 137   : Filename(Name), RemoveImmediately(true) {
 138     sys::RemoveFileOnSignal(Filename, nullptr);
 139   }
 140
 141   ~RemoveUniqueLockFileOnSignal() {
 142     if (!RemoveImmediately) {
 143       // Leave the signal handler enabled. It will be removed when the lock is
 144       // released.
 145       return;
 146     }
 147     sys::fs::remove(Filename);
 148     sys::DontRemoveFileOnSignal(Filename);
 149   }
 150
 151   void lockAcquired() { RemoveImmediately = false; }
 152 };
 153
 154 } // end anonymous namespace
 155
 156 LockFileManager::LockFileManager(StringRef FileName)
 157 {
 158   this->FileName = FileName;
 159   if (std::error_code EC = sys::fs::make_absolute(this->FileName)) {
 160     std::string S("failed to obtain absolute path for ");
 161     S.append(this->FileName.str());
 162     setError(EC, S);
 163     return;
 164   }
 165   LockFileName = this->FileName;
 166   LockFileName += ".lock";
 167
 168   // If the lock file already exists, don't bother to try to create our own
 169   // lock file; it won't work anyway. Just figure out who owns this lock file.
 170   if ((Owner = readLockFile(LockFileName)))
 171     return;
 172
 173   // Create a lock file that is unique to this instance.
 174   UniqueLockFileName = LockFileName;
 175   UniqueLockFileName += "-%%%%%%%%";
 176   int UniqueLockFileID;
 177   if (std::error_code EC = sys::fs::createUniqueFile(
 178           UniqueLockFileName, UniqueLockFileID, UniqueLockFileName)) {
 179     std::string S("failed to create unique file ");
 180     S.append(UniqueLockFileName.str());
 181     setError(EC, S);
 182     return;
 183   }
 184
 185   // Write our process ID to our unique lock file.
 186   {
 187     SmallString<256> HostID;
 188     if (auto EC = getHostID(HostID)) {
 189       setError(EC, "failed to get host id");
 190       return;
 191     }
 192
 193     raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
 194     Out << HostID << ' ';
 195 #if LLVM_ON_UNIX
 196     Out << getpid();
 197 #else
 198     Out << "1";
 199 #endif
 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(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(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 LockFileManager::waitForUnlock() {
 294   if (getState() != LFS_Shared)
 295     return Res_Success;
 296
 297 #ifdef _WIN32
 298   unsigned long Interval = 1;
 299 #else
 300   struct timespec Interval;
 301   Interval.tv_sec = 0;
 302   Interval.tv_nsec = 1000000;
 303 #endif
 304   // Don't wait more than 40s per iteration. Total timeout for the file
 305   // to appear is ~1.5 minutes.
 306   const unsigned MaxSeconds = 40;
 307   do {
 308     // Sleep for the designated interval, to allow the owning process time to
 309     // finish up and remove the lock file.
 310     // FIXME: Should we hook in to system APIs to get a notification when the
 311     // lock file is deleted?
 312 #ifdef _WIN32
 313     Sleep(Interval);
 314 #else
 315     nanosleep(&Interval, nullptr);
 316 #endif
 317
 318     if (sys::fs::access(LockFileName.c_str(), sys::fs::AccessMode::Exist) ==
 319         errc::no_such_file_or_directory) {
 320       // If the original file wasn't created, somone thought the lock was dead.
 321       if (!sys::fs::exists(FileName))
 322         return Res_OwnerDied;
 323       return Res_Success;
 324     }
 325
 326     // If the process owning the lock died without cleaning up, just bail out.
 327     if (!processStillExecuting((*Owner).first, (*Owner).second))
 328       return Res_OwnerDied;
 329
 330     // Exponentially increase the time we wait for the lock to be removed.
 331 #ifdef _WIN32
 332     Interval *= 2;
 333 #else
 334     Interval.tv_sec *= 2;
 335     Interval.tv_nsec *= 2;
 336     if (Interval.tv_nsec >= 1000000000) {
 337       ++Interval.tv_sec;
 338       Interval.tv_nsec -= 1000000000;
 339     }
 340 #endif
 341   } while (
 342 #ifdef _WIN32
 343            Interval < MaxSeconds * 1000
 344 #else
 345            Interval.tv_sec < (time_t)MaxSeconds
 346 #endif
 347            );
 348
 349   // Give up.
 350   return Res_Timeout;
 351 }
 352
 353 std::error_code LockFileManager::unsafeRemoveLockFile() {
 354   return sys::fs::remove(LockFileName);
 355 }