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/StringExtras.h"
11#include "llvm/Support/Errc.h"
12#include "llvm/Support/FileSystem.h"
13#include "llvm/Support/MemoryBuffer.h"
14#include "llvm/Support/raw_ostream.h"
15#include "llvm/Support/Signals.h"
16#include <sys/stat.h>
17#include <sys/types.h>
18#if LLVM_ON_WIN32
19#include <windows.h>
20#endif
21#if LLVM_ON_UNIX
22#include <unistd.h>
23#endif
24
25#if defined(__APPLE__) && defined(__MAC_OS_X_VERSION_MIN_REQUIRED) && (__MAC_OS_X_VERSION_MIN_REQUIRED > 1050)
26#define USE_OSX_GETHOSTUUID 1
27#else
28#define USE_OSX_GETHOSTUUID 0
29#endif
30
31#if USE_OSX_GETHOSTUUID
32#include <uuid/uuid.h>
33#endif
34using namespace llvm;
35
36/// \brief Attempt to read the lock file with the given name, if it exists.
37///
38/// \param LockFileName The name of the lock file to read.
39///
40/// \returns The process ID of the process that owns this lock file
41Optional<std::pair<std::string, int> >
42LockFileManager::readLockFile(StringRef LockFileName) {
43  // Read the owning host and PID out of the lock file. If it appears that the
44  // owning process is dead, the lock file is invalid.
45  ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
46      MemoryBuffer::getFile(LockFileName);
47  if (!MBOrErr) {
48    sys::fs::remove(LockFileName);
49    return None;
50  }
51  MemoryBuffer &MB = *MBOrErr.get();
52
53  StringRef Hostname;
54  StringRef PIDStr;
55  std::tie(Hostname, PIDStr) = getToken(MB.getBuffer(), " ");
56  PIDStr = PIDStr.substr(PIDStr.find_first_not_of(" "));
57  int PID;
58  if (!PIDStr.getAsInteger(10, PID)) {
59    auto Owner = std::make_pair(std::string(Hostname), PID);
60    if (processStillExecuting(Owner.first, Owner.second))
61      return Owner;
62  }
63
64  // Delete the lock file. It's invalid anyway.
65  sys::fs::remove(LockFileName);
66  return None;
67}
68
69static std::error_code getHostID(SmallVectorImpl<char> &HostID) {
70  HostID.clear();
71
72#if USE_OSX_GETHOSTUUID
73  // On OS X, use the more stable hardware UUID instead of hostname.
74  struct timespec wait = {1, 0}; // 1 second.
75  uuid_t uuid;
76  if (gethostuuid(uuid, &wait) != 0)
77    return std::error_code(errno, std::system_category());
78
79  uuid_string_t UUIDStr;
80  uuid_unparse(uuid, UUIDStr);
81  StringRef UUIDRef(UUIDStr);
82  HostID.append(UUIDRef.begin(), UUIDRef.end());
83
84#elif LLVM_ON_UNIX
85  char HostName[256];
86  HostName[255] = 0;
87  HostName[0] = 0;
88  gethostname(HostName, 255);
89  StringRef HostNameRef(HostName);
90  HostID.append(HostNameRef.begin(), HostNameRef.end());
91
92#else
93  StringRef Dummy("localhost");
94  HostID.append(Dummy.begin(), Dummy.end());
95#endif
96
97  return std::error_code();
98}
99
100bool LockFileManager::processStillExecuting(StringRef HostID, int PID) {
101#if LLVM_ON_UNIX && !defined(__ANDROID__)
102  SmallString<256> StoredHostID;
103  if (getHostID(StoredHostID))
104    return true; // Conservatively assume it's executing on error.
105
106  // Check whether the process is dead. If so, we're done.
107  if (StoredHostID == HostID && getsid(PID) == -1 && errno == ESRCH)
108    return false;
109#endif
110
111  return true;
112}
113
114namespace {
115/// An RAII helper object ensure that the unique lock file is removed.
116///
117/// Ensures that if there is an error or a signal before we finish acquiring the
118/// lock, the unique file will be removed. And if we successfully take the lock,
119/// the signal handler is left in place so that signals while the lock is held
120/// will remove the unique lock file. The caller should ensure there is a
121/// matching call to sys::DontRemoveFileOnSignal when the lock is released.
122class RemoveUniqueLockFileOnSignal {
123  StringRef Filename;
124  bool RemoveImmediately;
125public:
126  RemoveUniqueLockFileOnSignal(StringRef Name)
127  : Filename(Name), RemoveImmediately(true) {
128    sys::RemoveFileOnSignal(Filename, nullptr);
129  }
130  ~RemoveUniqueLockFileOnSignal() {
131    if (!RemoveImmediately) {
132      // Leave the signal handler enabled. It will be removed when the lock is
133      // released.
134      return;
135    }
136    sys::fs::remove(Filename);
137    sys::DontRemoveFileOnSignal(Filename);
138  }
139  void lockAcquired() { RemoveImmediately = false; }
140};
141} // end anonymous namespace
142
143LockFileManager::LockFileManager(StringRef FileName)
144{
145  this->FileName = FileName;
146  if (std::error_code EC = sys::fs::make_absolute(this->FileName)) {
147    Error = EC;
148    return;
149  }
150  LockFileName = this->FileName;
151  LockFileName += ".lock";
152
153  // If the lock file already exists, don't bother to try to create our own
154  // lock file; it won't work anyway. Just figure out who owns this lock file.
155  if ((Owner = readLockFile(LockFileName)))
156    return;
157
158  // Create a lock file that is unique to this instance.
159  UniqueLockFileName = LockFileName;
160  UniqueLockFileName += "-%%%%%%%%";
161  int UniqueLockFileID;
162  if (std::error_code EC = sys::fs::createUniqueFile(
163          UniqueLockFileName, UniqueLockFileID, UniqueLockFileName)) {
164    Error = EC;
165    return;
166  }
167
168  // Write our process ID to our unique lock file.
169  {
170    SmallString<256> HostID;
171    if (auto EC = getHostID(HostID)) {
172      Error = EC;
173      return;
174    }
175
176    raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
177    Out << HostID << ' ';
178#if LLVM_ON_UNIX
179    Out << getpid();
180#else
181    Out << "1";
182#endif
183    Out.close();
184
185    if (Out.has_error()) {
186      // We failed to write out PID, so make up an excuse, remove the
187      // unique lock file, and fail.
188      Error = make_error_code(errc::no_space_on_device);
189      sys::fs::remove(UniqueLockFileName);
190      return;
191    }
192  }
193
194  // Clean up the unique file on signal, which also releases the lock if it is
195  // held since the .lock symlink will point to a nonexistent file.
196  RemoveUniqueLockFileOnSignal RemoveUniqueFile(UniqueLockFileName);
197
198  while (1) {
199    // Create a link from the lock file name. If this succeeds, we're done.
200    std::error_code EC =
201        sys::fs::create_link(UniqueLockFileName, LockFileName);
202    if (!EC) {
203      RemoveUniqueFile.lockAcquired();
204      return;
205    }
206
207    if (EC != errc::file_exists) {
208      Error = EC;
209      return;
210    }
211
212    // Someone else managed to create the lock file first. Read the process ID
213    // from the lock file.
214    if ((Owner = readLockFile(LockFileName))) {
215      // Wipe out our unique lock file (it's useless now)
216      sys::fs::remove(UniqueLockFileName);
217      return;
218    }
219
220    if (!sys::fs::exists(LockFileName)) {
221      // The previous owner released the lock file before we could read it.
222      // Try to get ownership again.
223      continue;
224    }
225
226    // There is a lock file that nobody owns; try to clean it up and get
227    // ownership.
228    if ((EC = sys::fs::remove(LockFileName))) {
229      Error = EC;
230      return;
231    }
232  }
233}
234
235LockFileManager::LockFileState LockFileManager::getState() const {
236  if (Owner)
237    return LFS_Shared;
238
239  if (Error)
240    return LFS_Error;
241
242  return LFS_Owned;
243}
244
245LockFileManager::~LockFileManager() {
246  if (getState() != LFS_Owned)
247    return;
248
249  // Since we own the lock, remove the lock file and our own unique lock file.
250  sys::fs::remove(LockFileName);
251  sys::fs::remove(UniqueLockFileName);
252  // The unique file is now gone, so remove it from the signal handler. This
253  // matches a sys::RemoveFileOnSignal() in LockFileManager().
254  sys::DontRemoveFileOnSignal(UniqueLockFileName);
255}
256
257LockFileManager::WaitForUnlockResult LockFileManager::waitForUnlock() {
258  if (getState() != LFS_Shared)
259    return Res_Success;
260
261#if LLVM_ON_WIN32
262  unsigned long Interval = 1;
263#else
264  struct timespec Interval;
265  Interval.tv_sec = 0;
266  Interval.tv_nsec = 1000000;
267#endif
268  // Don't wait more than five minutes per iteration. Total timeout for the file
269  // to appear is ~8.5 mins.
270  const unsigned MaxSeconds = 5*60;
271  do {
272    // Sleep for the designated interval, to allow the owning process time to
273    // finish up and remove the lock file.
274    // FIXME: Should we hook in to system APIs to get a notification when the
275    // lock file is deleted?
276#if LLVM_ON_WIN32
277    Sleep(Interval);
278#else
279    nanosleep(&Interval, nullptr);
280#endif
281
282    if (sys::fs::access(LockFileName.c_str(), sys::fs::AccessMode::Exist) ==
283        errc::no_such_file_or_directory) {
284      // If the original file wasn't created, somone thought the lock was dead.
285      if (!sys::fs::exists(FileName))
286        return Res_OwnerDied;
287      return Res_Success;
288    }
289
290    // If the process owning the lock died without cleaning up, just bail out.
291    if (!processStillExecuting((*Owner).first, (*Owner).second))
292      return Res_OwnerDied;
293
294    // Exponentially increase the time we wait for the lock to be removed.
295#if LLVM_ON_WIN32
296    Interval *= 2;
297#else
298    Interval.tv_sec *= 2;
299    Interval.tv_nsec *= 2;
300    if (Interval.tv_nsec >= 1000000000) {
301      ++Interval.tv_sec;
302      Interval.tv_nsec -= 1000000000;
303    }
304#endif
305  } while (
306#if LLVM_ON_WIN32
307           Interval < MaxSeconds * 1000
308#else
309           Interval.tv_sec < (time_t)MaxSeconds
310#endif
311           );
312
313  // Give up.
314  return Res_Timeout;
315}
316
317std::error_code LockFileManager::unsafeRemoveLockFile() {
318  return sys::fs::remove(LockFileName);
319}
320