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
25 using 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
32 Optional<std::pair<std::string, int> >
readLockFile(StringRef LockFileName)33 LockFileManager::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
processStillExecuting(StringRef Hostname,int PID)60 bool 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
LockFileManager(StringRef FileName)74 LockFileManager::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
getState() const159 LockFileManager::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
~LockFileManager()169 LockFileManager::~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
waitForUnlock()178 LockFileManager::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