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/FileSystem.h"
13 #include "llvm/Support/MemoryBuffer.h"
14 #include "llvm/Support/raw_ostream.h"
15 #include <sys/stat.h>
16 #include <sys/types.h>
17 #if LLVM_ON_WIN32
18 #include <windows.h>
19 #endif
20 #if LLVM_ON_UNIX
21 #include <unistd.h>
22 #endif
23 using namespace llvm;
24
25 /// \brief Attempt to read the lock file with the given name, if it exists.
26 ///
27 /// \param LockFileName The name of the lock file to read.
28 ///
29 /// \returns The process ID of the process that owns this lock file
30 Optional<std::pair<std::string, int> >
readLockFile(StringRef LockFileName)31 LockFileManager::readLockFile(StringRef LockFileName) {
32 // Check whether the lock file exists. If not, clearly there's nothing
33 // to read, so we just return.
34 bool Exists = false;
35 if (sys::fs::exists(LockFileName, Exists) || !Exists)
36 return None;
37
38 // Read the owning host and PID out of the lock file. If it appears that the
39 // owning process is dead, the lock file is invalid.
40 OwningPtr<MemoryBuffer> MB;
41 if (MemoryBuffer::getFile(LockFileName, MB))
42 return None;
43
44 StringRef Hostname;
45 StringRef PIDStr;
46 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 return std::make_pair(std::string(Hostname), PID);
51
52 // Delete the lock file. It's invalid anyway.
53 sys::fs::remove(LockFileName);
54 return None;
55 }
56
processStillExecuting(StringRef Hostname,int PID)57 bool LockFileManager::processStillExecuting(StringRef Hostname, int PID) {
58 #if LLVM_ON_UNIX && !defined(__ANDROID__)
59 char MyHostname[256];
60 MyHostname[255] = 0;
61 MyHostname[0] = 0;
62 gethostname(MyHostname, 255);
63 // Check whether the process is dead. If so, we're done.
64 if (MyHostname == Hostname && getsid(PID) == -1 && errno == ESRCH)
65 return false;
66 #endif
67
68 return true;
69 }
70
LockFileManager(StringRef FileName)71 LockFileManager::LockFileManager(StringRef FileName)
72 {
73 this->FileName = FileName;
74 LockFileName = FileName;
75 LockFileName += ".lock";
76
77 // If the lock file already exists, don't bother to try to create our own
78 // lock file; it won't work anyway. Just figure out who owns this lock file.
79 if ((Owner = readLockFile(LockFileName)))
80 return;
81
82 // Create a lock file that is unique to this instance.
83 UniqueLockFileName = LockFileName;
84 UniqueLockFileName += "-%%%%%%%%";
85 int UniqueLockFileID;
86 if (error_code EC
87 = sys::fs::createUniqueFile(UniqueLockFileName.str(),
88 UniqueLockFileID,
89 UniqueLockFileName)) {
90 Error = EC;
91 return;
92 }
93
94 // Write our process ID to our unique lock file.
95 {
96 raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
97
98 #if LLVM_ON_UNIX
99 // FIXME: move getpid() call into LLVM
100 char hostname[256];
101 hostname[255] = 0;
102 hostname[0] = 0;
103 gethostname(hostname, 255);
104 Out << hostname << ' ' << getpid();
105 #else
106 Out << "localhost 1";
107 #endif
108 Out.close();
109
110 if (Out.has_error()) {
111 // We failed to write out PID, so make up an excuse, remove the
112 // unique lock file, and fail.
113 Error = make_error_code(errc::no_space_on_device);
114 bool Existed;
115 sys::fs::remove(UniqueLockFileName.c_str(), Existed);
116 return;
117 }
118 }
119
120 // Create a hard link from the lock file name. If this succeeds, we're done.
121 error_code EC
122 = sys::fs::create_hard_link(UniqueLockFileName.str(),
123 LockFileName.str());
124 if (EC == errc::success)
125 return;
126
127 // Creating the hard link failed.
128
129 #ifdef LLVM_ON_UNIX
130 // The creation of the hard link may appear to fail, but if stat'ing the
131 // unique file returns a link count of 2, then we can still declare success.
132 struct stat StatBuf;
133 if (stat(UniqueLockFileName.c_str(), &StatBuf) == 0 &&
134 StatBuf.st_nlink == 2)
135 return;
136 #endif
137
138 // Someone else managed to create the lock file first. Wipe out our unique
139 // lock file (it's useless now) and read the process ID from the lock file.
140 bool Existed;
141 sys::fs::remove(UniqueLockFileName.str(), Existed);
142 if ((Owner = readLockFile(LockFileName)))
143 return;
144
145 // There is a lock file that nobody owns; try to clean it up and report
146 // an error.
147 sys::fs::remove(LockFileName.str(), Existed);
148 Error = EC;
149 }
150
getState() const151 LockFileManager::LockFileState LockFileManager::getState() const {
152 if (Owner)
153 return LFS_Shared;
154
155 if (Error)
156 return LFS_Error;
157
158 return LFS_Owned;
159 }
160
~LockFileManager()161 LockFileManager::~LockFileManager() {
162 if (getState() != LFS_Owned)
163 return;
164
165 // Since we own the lock, remove the lock file and our own unique lock file.
166 bool Existed;
167 sys::fs::remove(LockFileName.str(), Existed);
168 sys::fs::remove(UniqueLockFileName.str(), Existed);
169 }
170
waitForUnlock()171 void LockFileManager::waitForUnlock() {
172 if (getState() != LFS_Shared)
173 return;
174
175 #if LLVM_ON_WIN32
176 unsigned long Interval = 1;
177 #else
178 struct timespec Interval;
179 Interval.tv_sec = 0;
180 Interval.tv_nsec = 1000000;
181 #endif
182 // Don't wait more than five minutes for the file to appear.
183 unsigned MaxSeconds = 300;
184 bool LockFileGone = false;
185 do {
186 // Sleep for the designated interval, to allow the owning process time to
187 // finish up and remove the lock file.
188 // FIXME: Should we hook in to system APIs to get a notification when the
189 // lock file is deleted?
190 #if LLVM_ON_WIN32
191 Sleep(Interval);
192 #else
193 nanosleep(&Interval, NULL);
194 #endif
195 bool Exists = false;
196 bool LockFileJustDisappeared = false;
197
198 // If the lock file is still expected to be there, check whether it still
199 // is.
200 if (!LockFileGone) {
201 if (!sys::fs::exists(LockFileName.str(), Exists) && !Exists) {
202 LockFileGone = true;
203 LockFileJustDisappeared = true;
204 Exists = false;
205 }
206 }
207
208 // If the lock file is no longer there, check if the original file is
209 // available now.
210 if (LockFileGone) {
211 if (!sys::fs::exists(FileName.str(), Exists) && Exists) {
212 return;
213 }
214
215 // The lock file is gone, so now we're waiting for the original file to
216 // show up. If this just happened, reset our waiting intervals and keep
217 // waiting.
218 if (LockFileJustDisappeared) {
219 MaxSeconds = 5;
220
221 #if LLVM_ON_WIN32
222 Interval = 1;
223 #else
224 Interval.tv_sec = 0;
225 Interval.tv_nsec = 1000000;
226 #endif
227 continue;
228 }
229 }
230
231 // If we're looking for the lock file to disappear, but the process
232 // owning the lock died without cleaning up, just bail out.
233 if (!LockFileGone &&
234 !processStillExecuting((*Owner).first, (*Owner).second)) {
235 return;
236 }
237
238 // Exponentially increase the time we wait for the lock to be removed.
239 #if LLVM_ON_WIN32
240 Interval *= 2;
241 #else
242 Interval.tv_sec *= 2;
243 Interval.tv_nsec *= 2;
244 if (Interval.tv_nsec >= 1000000000) {
245 ++Interval.tv_sec;
246 Interval.tv_nsec -= 1000000000;
247 }
248 #endif
249 } while (
250 #if LLVM_ON_WIN32
251 Interval < MaxSeconds * 1000
252 #else
253 Interval.tv_sec < (time_t)MaxSeconds
254 #endif
255 );
256
257 // Give up.
258 }
259