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/types.h>
14 #include <sys/stat.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 Optional<std::pair<std::string, int> >();
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 Optional<std::pair<std::string, int> >();
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 LockFileName = FileName;
68 LockFileName += ".lock";
69
70 // If the lock file already exists, don't bother to try to create our own
71 // lock file; it won't work anyway. Just figure out who owns this lock file.
72 if ((Owner = readLockFile(LockFileName)))
73 return;
74
75 // Create a lock file that is unique to this instance.
76 UniqueLockFileName = LockFileName;
77 UniqueLockFileName += "-%%%%%%%%";
78 int UniqueLockFileID;
79 if (error_code EC
80 = sys::fs::unique_file(UniqueLockFileName.str(),
81 UniqueLockFileID,
82 UniqueLockFileName,
83 /*makeAbsolute=*/false)) {
84 Error = EC;
85 return;
86 }
87
88 // Write our process ID to our unique lock file.
89 {
90 raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
91
92 #if LLVM_ON_UNIX
93 // FIXME: move getpid() call into LLVM
94 char hostname[256];
95 hostname[255] = 0;
96 hostname[0] = 0;
97 gethostname(hostname, 255);
98 Out << hostname << ' ' << getpid();
99 #else
100 Out << "localhost 1";
101 #endif
102 Out.close();
103
104 if (Out.has_error()) {
105 // We failed to write out PID, so make up an excuse, remove the
106 // unique lock file, and fail.
107 Error = make_error_code(errc::no_space_on_device);
108 bool Existed;
109 sys::fs::remove(UniqueLockFileName.c_str(), Existed);
110 return;
111 }
112 }
113
114 // Create a hard link from the lock file name. If this succeeds, we're done.
115 error_code EC
116 = sys::fs::create_hard_link(UniqueLockFileName.str(),
117 LockFileName.str());
118 if (EC == errc::success)
119 return;
120
121 // Creating the hard link failed.
122
123 #ifdef LLVM_ON_UNIX
124 // The creation of the hard link may appear to fail, but if stat'ing the
125 // unique file returns a link count of 2, then we can still declare success.
126 struct stat StatBuf;
127 if (stat(UniqueLockFileName.c_str(), &StatBuf) == 0 &&
128 StatBuf.st_nlink == 2)
129 return;
130 #endif
131
132 // Someone else managed to create the lock file first. Wipe out our unique
133 // lock file (it's useless now) and read the process ID from the lock file.
134 bool Existed;
135 sys::fs::remove(UniqueLockFileName.str(), Existed);
136 if ((Owner = readLockFile(LockFileName)))
137 return;
138
139 // There is a lock file that nobody owns; try to clean it up and report
140 // an error.
141 sys::fs::remove(LockFileName.str(), Existed);
142 Error = EC;
143 }
144
getState() const145 LockFileManager::LockFileState LockFileManager::getState() const {
146 if (Owner)
147 return LFS_Shared;
148
149 if (Error)
150 return LFS_Error;
151
152 return LFS_Owned;
153 }
154
~LockFileManager()155 LockFileManager::~LockFileManager() {
156 if (getState() != LFS_Owned)
157 return;
158
159 // Since we own the lock, remove the lock file and our own unique lock file.
160 bool Existed;
161 sys::fs::remove(LockFileName.str(), Existed);
162 sys::fs::remove(UniqueLockFileName.str(), Existed);
163 }
164
waitForUnlock()165 void LockFileManager::waitForUnlock() {
166 if (getState() != LFS_Shared)
167 return;
168
169 #if LLVM_ON_WIN32
170 unsigned long Interval = 1;
171 #else
172 struct timespec Interval;
173 Interval.tv_sec = 0;
174 Interval.tv_nsec = 1000000;
175 #endif
176 // Don't wait more than an hour for the file to appear.
177 const unsigned MaxSeconds = 3600;
178 do {
179 // Sleep for the designated interval, to allow the owning process time to
180 // finish up and remove the lock file.
181 // FIXME: Should we hook in to system APIs to get a notification when the
182 // lock file is deleted?
183 #if LLVM_ON_WIN32
184 Sleep(Interval);
185 #else
186 nanosleep(&Interval, NULL);
187 #endif
188 // If the file no longer exists, we're done.
189 bool Exists = false;
190 if (!sys::fs::exists(LockFileName.str(), Exists) && !Exists)
191 return;
192
193 if (!processStillExecuting((*Owner).first, (*Owner).second))
194 return;
195
196 // Exponentially increase the time we wait for the lock to be removed.
197 #if LLVM_ON_WIN32
198 Interval *= 2;
199 #else
200 Interval.tv_sec *= 2;
201 Interval.tv_nsec *= 2;
202 if (Interval.tv_nsec >= 1000000000) {
203 ++Interval.tv_sec;
204 Interval.tv_nsec -= 1000000000;
205 }
206 #endif
207 } while (
208 #if LLVM_ON_WIN32
209 Interval < MaxSeconds * 1000
210 #else
211 Interval.tv_sec < (time_t)MaxSeconds
212 #endif
213 );
214
215 // Give up.
216 }
217