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
43using 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
50Optional<std::pair<std::string, int> >
51LockFileManager::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
78static 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
109bool 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
123namespace {
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.
132class RemoveUniqueLockFileOnSignal {
133  StringRef Filename;
134  bool RemoveImmediately;
135public:
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
156LockFileManager::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
259LockFileManager::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
269std::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
281LockFileManager::~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
293LockFileManager::WaitForUnlockResult
294LockFileManager::waitForUnlock(const unsigned MaxSeconds) {
295  if (getState() != LFS_Shared)
296    return Res_Success;
297
298#ifdef _WIN32
299  unsigned long Interval = 1;
300#else
301  struct timespec Interval;
302  Interval.tv_sec = 0;
303  Interval.tv_nsec = 1000000;
304#endif
305  do {
306    // Sleep for the designated interval, to allow the owning process time to
307    // finish up and remove the lock file.
308    // FIXME: Should we hook in to system APIs to get a notification when the
309    // lock file is deleted?
310#ifdef _WIN32
311    Sleep(Interval);
312#else
313    nanosleep(&Interval, nullptr);
314#endif
315
316    if (sys::fs::access(LockFileName.c_str(), sys::fs::AccessMode::Exist) ==
317        errc::no_such_file_or_directory) {
318      // If the original file wasn't created, somone thought the lock was dead.
319      if (!sys::fs::exists(FileName))
320        return Res_OwnerDied;
321      return Res_Success;
322    }
323
324    // If the process owning the lock died without cleaning up, just bail out.
325    if (!processStillExecuting((*Owner).first, (*Owner).second))
326      return Res_OwnerDied;
327
328    // Exponentially increase the time we wait for the lock to be removed.
329#ifdef _WIN32
330    Interval *= 2;
331#else
332    Interval.tv_sec *= 2;
333    Interval.tv_nsec *= 2;
334    if (Interval.tv_nsec >= 1000000000) {
335      ++Interval.tv_sec;
336      Interval.tv_nsec -= 1000000000;
337    }
338#endif
339  } while (
340#ifdef _WIN32
341           Interval < MaxSeconds * 1000
342#else
343           Interval.tv_sec < (time_t)MaxSeconds
344#endif
345           );
346
347  // Give up.
348  return Res_Timeout;
349}
350
351std::error_code LockFileManager::unsafeRemoveLockFile() {
352  return sys::fs::remove(LockFileName);
353}
354