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
34 using 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
41 Optional<std::pair<std::string, int> >
readLockFile(StringRef LockFileName)42 LockFileManager::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
getHostID(SmallVectorImpl<char> & HostID)69 static 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
processStillExecuting(StringRef HostID,int PID)100 bool 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
114 namespace {
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.
122 class RemoveUniqueLockFileOnSignal {
123 StringRef Filename;
124 bool RemoveImmediately;
125 public:
RemoveUniqueLockFileOnSignal(StringRef Name)126 RemoveUniqueLockFileOnSignal(StringRef Name)
127 : Filename(Name), RemoveImmediately(true) {
128 sys::RemoveFileOnSignal(Filename, nullptr);
129 }
~RemoveUniqueLockFileOnSignal()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 }
lockAcquired()139 void lockAcquired() { RemoveImmediately = false; }
140 };
141 } // end anonymous namespace
142
LockFileManager(StringRef FileName)143 LockFileManager::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
getState() const235 LockFileManager::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
~LockFileManager()245 LockFileManager::~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
waitForUnlock()257 LockFileManager::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
unsafeRemoveLockFile()317 std::error_code LockFileManager::unsafeRemoveLockFile() {
318 return sys::fs::remove(LockFileName);
319 }
320