llvm/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/SmallVector.h"
  11 #include "llvm/ADT/StringExtras.h"
  12 #include "llvm/Config/llvm-config.h" // for LLVM_ON_UNIX
  13 #include "llvm/Support/Errc.h"
  14 #include "llvm/Support/ErrorOr.h"
  15 #include "llvm/Support/ExponentialBackoff.h"
  16 #include "llvm/Support/FileSystem.h"
  17 #include "llvm/Support/MemoryBuffer.h"
  18 #include "llvm/Support/Process.h"
  19 #include "llvm/Support/Signals.h"
  20 #include "llvm/Support/raw_ostream.h"
  21 #include <cerrno>
  22 #include <chrono>
  23 #include <ctime>
  24 #include <memory>
  25 #include <sys/stat.h>
  26 #include <sys/types.h>
  27 #include <system_error>
  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 errnoAsErrorCode();
  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));
 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       // Don't call report_fatal_error.
 209       Out.clear_error();
 210       return;
 211     }
 212   }
 213
 214   // Clean up the unique file on signal, which also releases the lock if it is
 215   // held since the .lock symlink will point to a nonexistent file.
 216   RemoveUniqueLockFileOnSignal RemoveUniqueFile(UniqueLockFileName);
 217
 218   while (true) {
 219     // Create a link from the lock file name. If this succeeds, we're done.
 220     std::error_code EC =
 221         sys::fs::create_link(UniqueLockFileName, LockFileName);
 222     if (!EC) {
 223       RemoveUniqueFile.lockAcquired();
 224       return;
 225     }
 226
 227     if (EC != errc::file_exists) {
 228       std::string S("failed to create link ");
 229       raw_string_ostream OSS(S);
 230       OSS << LockFileName.str() << " to " << UniqueLockFileName.str();
 231       setError(EC, S);
 232       return;
 233     }
 234
 235     // Someone else managed to create the lock file first. Read the process ID
 236     // from the lock file.
 237     if ((Owner = readLockFile(LockFileName))) {
 238       // Wipe out our unique lock file (it's useless now)
 239       sys::fs::remove(UniqueLockFileName);
 240       return;
 241     }
 242
 243     if (!sys::fs::exists(LockFileName)) {
 244       // The previous owner released the lock file before we could read it.
 245       // Try to get ownership again.
 246       continue;
 247     }
 248
 249     // There is a lock file that nobody owns; try to clean it up and get
 250     // ownership.
 251     if ((EC = sys::fs::remove(LockFileName))) {
 252       std::string S("failed to remove lockfile ");
 253       S.append(std::string(UniqueLockFileName));
 254       setError(EC, S);
 255       return;
 256     }
 257   }
 258 }
 259
 260 LockFileManager::LockFileState LockFileManager::getState() const {
 261   if (Owner)
 262     return LFS_Shared;
 263
 264   if (ErrorCode)
 265     return LFS_Error;
 266
 267   return LFS_Owned;
 268 }
 269
 270 std::string LockFileManager::getErrorMessage() const {
 271   if (ErrorCode) {
 272     std::string Str(ErrorDiagMsg);
 273     std::string ErrCodeMsg = ErrorCode.message();
 274     raw_string_ostream OSS(Str);
 275     if (!ErrCodeMsg.empty())
 276       OSS << ": " << ErrCodeMsg;
 277     return Str;
 278   }
 279   return "";
 280 }
 281
 282 LockFileManager::~LockFileManager() {
 283   if (getState() != LFS_Owned)
 284     return;
 285
 286   // Since we own the lock, remove the lock file and our own unique lock file.
 287   sys::fs::remove(LockFileName);
 288   sys::fs::remove(UniqueLockFileName);
 289   // The unique file is now gone, so remove it from the signal handler. This
 290   // matches a sys::RemoveFileOnSignal() in LockFileManager().
 291   sys::DontRemoveFileOnSignal(UniqueLockFileName);
 292 }
 293
 294 LockFileManager::WaitForUnlockResult
 295 LockFileManager::waitForUnlock(const unsigned MaxSeconds) {
 296   if (getState() != LFS_Shared)
 297     return Res_Success;
 298
 299   // Since we don't yet have an event-based method to wait for the lock file,
 300   // use randomized exponential backoff, similar to Ethernet collision
 301   // algorithm. This improves performance on machines with high core counts
 302   // when the file lock is heavily contended by multiple clang processes
 303   using namespace std::chrono_literals;
 304   ExponentialBackoff Backoff(std::chrono::seconds(MaxSeconds), 10ms, 500ms);
 305
 306   // Wait first as this is only called when the lock is known to be held.
 307   while (Backoff.waitForNextAttempt()) {
 308     // FIXME: implement event-based waiting
 309     if (sys::fs::access(LockFileName.c_str(), sys::fs::AccessMode::Exist) ==
 310         errc::no_such_file_or_directory) {
 311       // If the original file wasn't created, somone thought the lock was dead.
 312       if (!sys::fs::exists(FileName))
 313         return Res_OwnerDied;
 314       return Res_Success;
 315     }
 316
 317     // If the process owning the lock died without cleaning up, just bail out.
 318     if (!processStillExecuting((*Owner).first, (*Owner).second))
 319       return Res_OwnerDied;
 320   }
 321
 322   // Give up.
 323   return Res_Timeout;
 324 }
 325
 326 std::error_code LockFileManager::unsafeRemoveLockFile() {
 327   return sys::fs::remove(LockFileName);
 328 }