LLVM  9.0.0svn
LockFileManager.cpp
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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 
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"
17 #include "llvm/Support/Signals.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
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.
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 
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 
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 
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) ==
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 
354  return sys::fs::remove(LockFileName);
355 }
static std::error_code getHostID(SmallVectorImpl< char > &HostID)
Represents either an error or a value T.
Definition: ErrorOr.h:56
LLVM_NODISCARD std::string str() const
str - Get the contents as an std::string.
Definition: StringRef.h:218
StringRef getBuffer() const
Definition: MemoryBuffer.h:63
This class represents lattice values for constants.
Definition: AllocatorList.h:23
std::error_code createUniqueFile(const Twine &Model, int &ResultFD, SmallVectorImpl< char > &ResultPath, unsigned Mode=all_read|all_write)
Create a uniquely named file.
Definition: Path.cpp:767
amdgpu Simplify well known AMD library false FunctionCallee Value const Twine & Name
WaitForUnlockResult
Describes the result of waiting for the owner to release the lock.
Interval Class - An Interval is a set of nodes defined such that every node in the interval has all o...
Definition: Interval.h:36
std::error_code remove(const Twine &path, bool IgnoreNonExisting=true)
Remove path.
std::string getErrorMessage() const
Get error message, or "" if there is no error.
The lock was released successfully.
void setError(const std::error_code &EC, StringRef ErrorMsg="")
Set error and error message.
std::error_code error() const
Definition: raw_ostream.h:445
void make_absolute(const Twine &current_directory, SmallVectorImpl< char > &path)
Make path an absolute path.
Definition: Path.cpp:853
An error occurred while trying to create or find the lock file.
LLVM_NODISCARD StringRef substr(size_t Start, size_t N=npos) const
Return a reference to the substring from [Start, Start + N).
Definition: StringRef.h:578
std::pair< StringRef, StringRef > getToken(StringRef Source, StringRef Delimiters=" \\\)
getToken - This function extracts one token from source, ignoring any leading characters that appear ...
std::error_code unsafeRemoveLockFile()
Remove the lock file.
std::error_code create_link(const Twine &to, const Twine &from)
Create a link from from to to.
LockFileState getState() const
Determine the state of the lock file.
LockFileState
Describes the state of a lock file.
void DontRemoveFileOnSignal(StringRef Filename)
This function removes a file from the list of files to be removed on signal delivery.
std::string & str()
Flushes the stream contents to the target string and returns the string&#39;s reference.
Definition: raw_ostream.h:498
bool has_error() const
Return the value of the flag in this raw_fd_ostream indicating whether an output error has been encou...
Definition: raw_ostream.h:451
Reached timeout while waiting for the owner to release the lock.
bool RemoveFileOnSignal(StringRef Filename, std::string *ErrMsg=nullptr)
This function registers signal handlers to ensure that if a signal gets delivered that the named file...
This interface provides simple read-only access to a block of memory, and provides simple methods for...
Definition: MemoryBuffer.h:41
iterator begin() const
Definition: StringRef.h:101
void append(in_iter in_start, in_iter in_end)
Add the specified range to the end of the SmallVector.
Definition: SmallVector.h:387
Owner died while holding the lock.
A raw_ostream that writes to a file descriptor.
Definition: raw_ostream.h:365
void close()
Manually flush the stream and close the file.
Provides ErrorOr<T> smart pointer.
static ErrorOr< std::unique_ptr< MemoryBuffer > > getFile(const Twine &Filename, int64_t FileSize=-1, bool RequiresNullTerminator=true, bool IsVolatile=false)
Open the specified file as a MemoryBuffer, returning a new MemoryBuffer if successful, otherwise returning null.
A raw_ostream that writes to an std::string.
Definition: raw_ostream.h:482
The lock file has been created and is owned by this instance of the object.
std::error_code access(const Twine &Path, AccessMode Mode)
Can the file be accessed?
WaitForUnlockResult waitForUnlock()
For a shared lock, wait until the owner releases the lock.
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:48
The lock file already exists and is owned by some other instance.
bool exists(const basic_file_status &status)
Does file exist?
Definition: Path.cpp:1025
iterator end() const
Definition: StringRef.h:103
reference get()
Definition: ErrorOr.h:156
raw_ostream::uuid_t uuid_t
Definition: MachOYAML.h:268