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/Errc.h"
13#include "llvm/Support/FileSystem.h"
14#include "llvm/Support/MemoryBuffer.h"
15#include "llvm/Support/Path.h"
16#include "llvm/Support/raw_ostream.h"
17#include <sys/stat.h>
18#include <sys/types.h>
19#if LLVM_ON_WIN32
20#include <windows.h>
21#endif
22#if LLVM_ON_UNIX
23#include <unistd.h>
24#endif
25using namespace llvm;
26
27/// \brief Attempt to read the lock file with the given name, if it exists.
28///
29/// \param LockFileName The name of the lock file to read.
30///
31/// \returns The process ID of the process that owns this lock file
32Optional<std::pair<std::string, int> >
33LockFileManager::readLockFile(StringRef LockFileName) {
34  // Read the owning host and PID out of the lock file. If it appears that the
35  // owning process is dead, the lock file is invalid.
36  ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
37      MemoryBuffer::getFile(LockFileName);
38  if (!MBOrErr) {
39    sys::fs::remove(LockFileName);
40    return None;
41  }
42  std::unique_ptr<MemoryBuffer> MB = std::move(MBOrErr.get());
43
44  StringRef Hostname;
45  StringRef PIDStr;
46  std::tie(Hostname, PIDStr) = getToken(MB->getBuffer(), " ");
47  PIDStr = PIDStr.substr(PIDStr.find_first_not_of(" "));
48  int PID;
49  if (!PIDStr.getAsInteger(10, PID)) {
50    auto Owner = std::make_pair(std::string(Hostname), PID);
51    if (processStillExecuting(Owner.first, Owner.second))
52      return Owner;
53  }
54
55  // Delete the lock file. It's invalid anyway.
56  sys::fs::remove(LockFileName);
57  return None;
58}
59
60bool LockFileManager::processStillExecuting(StringRef Hostname, int PID) {
61#if LLVM_ON_UNIX && !defined(__ANDROID__)
62  char MyHostname[256];
63  MyHostname[255] = 0;
64  MyHostname[0] = 0;
65  gethostname(MyHostname, 255);
66  // Check whether the process is dead. If so, we're done.
67  if (MyHostname == Hostname && getsid(PID) == -1 && errno == ESRCH)
68    return false;
69#endif
70
71  return true;
72}
73
74LockFileManager::LockFileManager(StringRef FileName)
75{
76  this->FileName = FileName;
77  if (std::error_code EC = sys::fs::make_absolute(this->FileName)) {
78    Error = EC;
79    return;
80  }
81  LockFileName = this->FileName;
82  LockFileName += ".lock";
83
84  // If the lock file already exists, don't bother to try to create our own
85  // lock file; it won't work anyway. Just figure out who owns this lock file.
86  if ((Owner = readLockFile(LockFileName)))
87    return;
88
89  // Create a lock file that is unique to this instance.
90  UniqueLockFileName = LockFileName;
91  UniqueLockFileName += "-%%%%%%%%";
92  int UniqueLockFileID;
93  if (std::error_code EC = sys::fs::createUniqueFile(
94          UniqueLockFileName.str(), UniqueLockFileID, UniqueLockFileName)) {
95    Error = EC;
96    return;
97  }
98
99  // Write our process ID to our unique lock file.
100  {
101    raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
102
103#if LLVM_ON_UNIX
104    // FIXME: move getpid() call into LLVM
105    char hostname[256];
106    hostname[255] = 0;
107    hostname[0] = 0;
108    gethostname(hostname, 255);
109    Out << hostname << ' ' << getpid();
110#else
111    Out << "localhost 1";
112#endif
113    Out.close();
114
115    if (Out.has_error()) {
116      // We failed to write out PID, so make up an excuse, remove the
117      // unique lock file, and fail.
118      Error = make_error_code(errc::no_space_on_device);
119      sys::fs::remove(UniqueLockFileName.c_str());
120      return;
121    }
122  }
123
124  while (1) {
125    // Create a link from the lock file name. If this succeeds, we're done.
126    std::error_code EC =
127        sys::fs::create_link(UniqueLockFileName.str(), LockFileName.str());
128    if (!EC)
129      return;
130
131    if (EC != errc::file_exists) {
132      Error = EC;
133      return;
134    }
135
136    // Someone else managed to create the lock file first. Read the process ID
137    // from the lock file.
138    if ((Owner = readLockFile(LockFileName))) {
139      // Wipe out our unique lock file (it's useless now)
140      sys::fs::remove(UniqueLockFileName.str());
141      return;
142    }
143
144    if (!sys::fs::exists(LockFileName.str())) {
145      // The previous owner released the lock file before we could read it.
146      // Try to get ownership again.
147      continue;
148    }
149
150    // There is a lock file that nobody owns; try to clean it up and get
151    // ownership.
152    if ((EC = sys::fs::remove(LockFileName.str()))) {
153      Error = EC;
154      return;
155    }
156  }
157}
158
159LockFileManager::LockFileState LockFileManager::getState() const {
160  if (Owner)
161    return LFS_Shared;
162
163  if (Error)
164    return LFS_Error;
165
166  return LFS_Owned;
167}
168
169LockFileManager::~LockFileManager() {
170  if (getState() != LFS_Owned)
171    return;
172
173  // Since we own the lock, remove the lock file and our own unique lock file.
174  sys::fs::remove(LockFileName.str());
175  sys::fs::remove(UniqueLockFileName.str());
176}
177
178LockFileManager::WaitForUnlockResult LockFileManager::waitForUnlock() {
179  if (getState() != LFS_Shared)
180    return Res_Success;
181
182#if LLVM_ON_WIN32
183  unsigned long Interval = 1;
184#else
185  struct timespec Interval;
186  Interval.tv_sec = 0;
187  Interval.tv_nsec = 1000000;
188#endif
189  // Don't wait more than five minutes for the file to appear.
190  unsigned MaxSeconds = 300;
191  bool LockFileGone = false;
192  do {
193    // Sleep for the designated interval, to allow the owning process time to
194    // finish up and remove the lock file.
195    // FIXME: Should we hook in to system APIs to get a notification when the
196    // lock file is deleted?
197#if LLVM_ON_WIN32
198    Sleep(Interval);
199#else
200    nanosleep(&Interval, nullptr);
201#endif
202    bool LockFileJustDisappeared = false;
203
204    // If the lock file is still expected to be there, check whether it still
205    // is.
206    if (!LockFileGone) {
207      bool Exists;
208      if (!sys::fs::exists(LockFileName.str(), Exists) && !Exists) {
209        LockFileGone = true;
210        LockFileJustDisappeared = true;
211      }
212    }
213
214    // If the lock file is no longer there, check if the original file is
215    // available now.
216    if (LockFileGone) {
217      if (sys::fs::exists(FileName.str())) {
218        return Res_Success;
219      }
220
221      // The lock file is gone, so now we're waiting for the original file to
222      // show up. If this just happened, reset our waiting intervals and keep
223      // waiting.
224      if (LockFileJustDisappeared) {
225        MaxSeconds = 5;
226
227#if LLVM_ON_WIN32
228        Interval = 1;
229#else
230        Interval.tv_sec = 0;
231        Interval.tv_nsec = 1000000;
232#endif
233        continue;
234      }
235    }
236
237    // If we're looking for the lock file to disappear, but the process
238    // owning the lock died without cleaning up, just bail out.
239    if (!LockFileGone &&
240        !processStillExecuting((*Owner).first, (*Owner).second)) {
241      return Res_OwnerDied;
242    }
243
244    // Exponentially increase the time we wait for the lock to be removed.
245#if LLVM_ON_WIN32
246    Interval *= 2;
247#else
248    Interval.tv_sec *= 2;
249    Interval.tv_nsec *= 2;
250    if (Interval.tv_nsec >= 1000000000) {
251      ++Interval.tv_sec;
252      Interval.tv_nsec -= 1000000000;
253    }
254#endif
255  } while (
256#if LLVM_ON_WIN32
257           Interval < MaxSeconds * 1000
258#else
259           Interval.tv_sec < (time_t)MaxSeconds
260#endif
261           );
262
263  // Give up.
264  return Res_Timeout;
265}
266