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> >
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   MemoryBuffer &MB = *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 
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 
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 
159 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 
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 
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 one minute for the file to appear.
190   const unsigned MaxSeconds = 60;
191   do {
192     // Sleep for the designated interval, to allow the owning process time to
193     // finish up and remove the lock file.
194     // FIXME: Should we hook in to system APIs to get a notification when the
195     // lock file is deleted?
196 #if LLVM_ON_WIN32
197     Sleep(Interval);
198 #else
199     nanosleep(&Interval, nullptr);
200 #endif
201 
202     if (sys::fs::access(LockFileName.c_str(), sys::fs::AccessMode::Exist) ==
203         errc::no_such_file_or_directory) {
204       // If the original file wasn't created, somone thought the lock was dead.
205       if (!sys::fs::exists(FileName.str()))
206         return Res_OwnerDied;
207       return Res_Success;
208     }
209 
210     // If the process owning the lock died without cleaning up, just bail out.
211     if (!processStillExecuting((*Owner).first, (*Owner).second))
212       return Res_OwnerDied;
213 
214     // Exponentially increase the time we wait for the lock to be removed.
215 #if LLVM_ON_WIN32
216     Interval *= 2;
217 #else
218     Interval.tv_sec *= 2;
219     Interval.tv_nsec *= 2;
220     if (Interval.tv_nsec >= 1000000000) {
221       ++Interval.tv_sec;
222       Interval.tv_nsec -= 1000000000;
223     }
224 #endif
225   } while (
226 #if LLVM_ON_WIN32
227            Interval < MaxSeconds * 1000
228 #else
229            Interval.tv_sec < (time_t)MaxSeconds
230 #endif
231            );
232 
233   // Give up.
234   return Res_Timeout;
235 }
236 
237 std::error_code LockFileManager::unsafeRemoveLockFile() {
238   return sys::fs::remove(LockFileName.str());
239 }
240