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/Support/FileSystem.h"
11 #include "llvm/Support/raw_ostream.h"
12 #include <fstream>
13 #include <sys/stat.h>
14 #include <sys/types.h>
15 #if LLVM_ON_WIN32
16 #include <windows.h>
17 #endif
18 #if LLVM_ON_UNIX
19 #include <unistd.h>
20 #endif
21 using namespace llvm;
22
23 /// \brief Attempt to read the lock file with the given name, if it exists.
24 ///
25 /// \param LockFileName The name of the lock file to read.
26 ///
27 /// \returns The process ID of the process that owns this lock file
28 Optional<std::pair<std::string, int> >
readLockFile(StringRef LockFileName)29 LockFileManager::readLockFile(StringRef LockFileName) {
30 // Check whether the lock file exists. If not, clearly there's nothing
31 // to read, so we just return.
32 bool Exists = false;
33 if (sys::fs::exists(LockFileName, Exists) || !Exists)
34 return None;
35
36 // Read the owning host and PID out of the lock file. If it appears that the
37 // owning process is dead, the lock file is invalid.
38 int PID = 0;
39 std::string Hostname;
40 std::ifstream Input(LockFileName.str().c_str());
41 if (Input >> Hostname >> PID && PID > 0 &&
42 processStillExecuting(Hostname, PID))
43 return std::make_pair(Hostname, PID);
44
45 // Delete the lock file. It's invalid anyway.
46 bool Existed;
47 sys::fs::remove(LockFileName, Existed);
48 return None;
49 }
50
processStillExecuting(StringRef Hostname,int PID)51 bool LockFileManager::processStillExecuting(StringRef Hostname, int PID) {
52 #if LLVM_ON_UNIX && !defined(__ANDROID__)
53 char MyHostname[256];
54 MyHostname[255] = 0;
55 MyHostname[0] = 0;
56 gethostname(MyHostname, 255);
57 // Check whether the process is dead. If so, we're done.
58 if (MyHostname == Hostname && getsid(PID) == -1 && errno == ESRCH)
59 return false;
60 #endif
61
62 return true;
63 }
64
LockFileManager(StringRef FileName)65 LockFileManager::LockFileManager(StringRef FileName)
66 {
67 this->FileName = FileName;
68 LockFileName = FileName;
69 LockFileName += ".lock";
70
71 // If the lock file already exists, don't bother to try to create our own
72 // lock file; it won't work anyway. Just figure out who owns this lock file.
73 if ((Owner = readLockFile(LockFileName)))
74 return;
75
76 // Create a lock file that is unique to this instance.
77 UniqueLockFileName = LockFileName;
78 UniqueLockFileName += "-%%%%%%%%";
79 int UniqueLockFileID;
80 if (error_code EC
81 = sys::fs::unique_file(UniqueLockFileName.str(),
82 UniqueLockFileID,
83 UniqueLockFileName,
84 /*makeAbsolute=*/false)) {
85 Error = EC;
86 return;
87 }
88
89 // Write our process ID to our unique lock file.
90 {
91 raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
92
93 #if LLVM_ON_UNIX
94 // FIXME: move getpid() call into LLVM
95 char hostname[256];
96 hostname[255] = 0;
97 hostname[0] = 0;
98 gethostname(hostname, 255);
99 Out << hostname << ' ' << getpid();
100 #else
101 Out << "localhost 1";
102 #endif
103 Out.close();
104
105 if (Out.has_error()) {
106 // We failed to write out PID, so make up an excuse, remove the
107 // unique lock file, and fail.
108 Error = make_error_code(errc::no_space_on_device);
109 bool Existed;
110 sys::fs::remove(UniqueLockFileName.c_str(), Existed);
111 return;
112 }
113 }
114
115 // Create a hard link from the lock file name. If this succeeds, we're done.
116 error_code EC
117 = sys::fs::create_hard_link(UniqueLockFileName.str(),
118 LockFileName.str());
119 if (EC == errc::success)
120 return;
121
122 // Creating the hard link failed.
123
124 #ifdef LLVM_ON_UNIX
125 // The creation of the hard link may appear to fail, but if stat'ing the
126 // unique file returns a link count of 2, then we can still declare success.
127 struct stat StatBuf;
128 if (stat(UniqueLockFileName.c_str(), &StatBuf) == 0 &&
129 StatBuf.st_nlink == 2)
130 return;
131 #endif
132
133 // Someone else managed to create the lock file first. Wipe out our unique
134 // lock file (it's useless now) and read the process ID from the lock file.
135 bool Existed;
136 sys::fs::remove(UniqueLockFileName.str(), Existed);
137 if ((Owner = readLockFile(LockFileName)))
138 return;
139
140 // There is a lock file that nobody owns; try to clean it up and report
141 // an error.
142 sys::fs::remove(LockFileName.str(), Existed);
143 Error = EC;
144 }
145
getState() const146 LockFileManager::LockFileState LockFileManager::getState() const {
147 if (Owner)
148 return LFS_Shared;
149
150 if (Error)
151 return LFS_Error;
152
153 return LFS_Owned;
154 }
155
~LockFileManager()156 LockFileManager::~LockFileManager() {
157 if (getState() != LFS_Owned)
158 return;
159
160 // Since we own the lock, remove the lock file and our own unique lock file.
161 bool Existed;
162 sys::fs::remove(LockFileName.str(), Existed);
163 sys::fs::remove(UniqueLockFileName.str(), Existed);
164 }
165
waitForUnlock()166 void LockFileManager::waitForUnlock() {
167 if (getState() != LFS_Shared)
168 return;
169
170 #if LLVM_ON_WIN32
171 unsigned long Interval = 1;
172 #else
173 struct timespec Interval;
174 Interval.tv_sec = 0;
175 Interval.tv_nsec = 1000000;
176 #endif
177 // Don't wait more than an hour for the file to appear.
178 const unsigned MaxSeconds = 3600;
179 bool LockFileGone = false;
180 do {
181 // Sleep for the designated interval, to allow the owning process time to
182 // finish up and remove the lock file.
183 // FIXME: Should we hook in to system APIs to get a notification when the
184 // lock file is deleted?
185 #if LLVM_ON_WIN32
186 Sleep(Interval);
187 #else
188 nanosleep(&Interval, NULL);
189 #endif
190 // If the lock file no longer exists, wait for the actual file.
191 bool Exists = false;
192 if (!LockFileGone) {
193 if (!sys::fs::exists(LockFileName.str(), Exists) && !Exists) {
194 LockFileGone = true;
195 Exists = false;
196 }
197 }
198 if (LockFileGone) {
199 if (!sys::fs::exists(FileName.str(), Exists) && Exists)
200 return;
201 }
202
203 if (!processStillExecuting((*Owner).first, (*Owner).second))
204 return;
205
206 // Exponentially increase the time we wait for the lock to be removed.
207 #if LLVM_ON_WIN32
208 Interval *= 2;
209 #else
210 Interval.tv_sec *= 2;
211 Interval.tv_nsec *= 2;
212 if (Interval.tv_nsec >= 1000000000) {
213 ++Interval.tv_sec;
214 Interval.tv_nsec -= 1000000000;
215 }
216 #endif
217 } while (
218 #if LLVM_ON_WIN32
219 Interval < MaxSeconds * 1000
220 #else
221 Interval.tv_sec < (time_t)MaxSeconds
222 #endif
223 );
224
225 // Give up.
226 }
227