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/StringExtras.h"
11 #include "llvm/Support/Errc.h"
12 #include "llvm/Support/FileSystem.h"
13 #include "llvm/Support/MemoryBuffer.h"
14 #include "llvm/Support/raw_ostream.h"
15 #include "llvm/Support/Signals.h"
16 #include <sys/stat.h>
17 #include <sys/types.h>
18 #if LLVM_ON_WIN32
19 #include <windows.h>
20 #endif
21 #if LLVM_ON_UNIX
22 #include <unistd.h>
23 #endif
24 using namespace llvm;
25 
26 /// \brief Attempt to read the lock file with the given name, if it exists.
27 ///
28 /// \param LockFileName The name of the lock file to read.
29 ///
30 /// \returns The process ID of the process that owns this lock file
31 Optional<std::pair<std::string, int> >
32 LockFileManager::readLockFile(StringRef LockFileName) {
33   // Read the owning host and PID out of the lock file. If it appears that the
34   // owning process is dead, the lock file is invalid.
35   ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
36       MemoryBuffer::getFile(LockFileName);
37   if (!MBOrErr) {
38     sys::fs::remove(LockFileName);
39     return None;
40   }
41   MemoryBuffer &MB = *MBOrErr.get();
42 
43   StringRef Hostname;
44   StringRef PIDStr;
45   std::tie(Hostname, PIDStr) = getToken(MB.getBuffer(), " ");
46   PIDStr = PIDStr.substr(PIDStr.find_first_not_of(" "));
47   int PID;
48   if (!PIDStr.getAsInteger(10, PID)) {
49     auto Owner = std::make_pair(std::string(Hostname), PID);
50     if (processStillExecuting(Owner.first, Owner.second))
51       return Owner;
52   }
53 
54   // Delete the lock file. It's invalid anyway.
55   sys::fs::remove(LockFileName);
56   return None;
57 }
58 
59 bool LockFileManager::processStillExecuting(StringRef Hostname, int PID) {
60 #if LLVM_ON_UNIX && !defined(__ANDROID__)
61   char MyHostname[256];
62   MyHostname[255] = 0;
63   MyHostname[0] = 0;
64   gethostname(MyHostname, 255);
65   // Check whether the process is dead. If so, we're done.
66   if (MyHostname == Hostname && getsid(PID) == -1 && errno == ESRCH)
67     return false;
68 #endif
69 
70   return true;
71 }
72 
73 namespace {
74 /// An RAII helper object ensure that the unique lock file is removed.
75 ///
76 /// Ensures that if there is an error or a signal before we finish acquiring the
77 /// lock, the unique file will be removed. And if we successfully take the lock,
78 /// the signal handler is left in place so that signals while the lock is held
79 /// will remove the unique lock file. The caller should ensure there is a
80 /// matching call to sys::DontRemoveFileOnSignal when the lock is released.
81 class RemoveUniqueLockFileOnSignal {
82   StringRef Filename;
83   bool RemoveImmediately;
84 public:
85   RemoveUniqueLockFileOnSignal(StringRef Name)
86   : Filename(Name), RemoveImmediately(true) {
87     sys::RemoveFileOnSignal(Filename, nullptr);
88   }
89   ~RemoveUniqueLockFileOnSignal() {
90     if (!RemoveImmediately) {
91       // Leave the signal handler enabled. It will be removed when the lock is
92       // released.
93       return;
94     }
95     sys::fs::remove(Filename);
96     sys::DontRemoveFileOnSignal(Filename);
97   }
98   void lockAcquired() { RemoveImmediately = false; }
99 };
100 } // end anonymous namespace
101 
102 LockFileManager::LockFileManager(StringRef FileName)
103 {
104   this->FileName = FileName;
105   if (std::error_code EC = sys::fs::make_absolute(this->FileName)) {
106     Error = EC;
107     return;
108   }
109   LockFileName = this->FileName;
110   LockFileName += ".lock";
111 
112   // If the lock file already exists, don't bother to try to create our own
113   // lock file; it won't work anyway. Just figure out who owns this lock file.
114   if ((Owner = readLockFile(LockFileName)))
115     return;
116 
117   // Create a lock file that is unique to this instance.
118   UniqueLockFileName = LockFileName;
119   UniqueLockFileName += "-%%%%%%%%";
120   int UniqueLockFileID;
121   if (std::error_code EC = sys::fs::createUniqueFile(
122           UniqueLockFileName, UniqueLockFileID, UniqueLockFileName)) {
123     Error = EC;
124     return;
125   }
126 
127   // Write our process ID to our unique lock file.
128   {
129     raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
130 
131 #if LLVM_ON_UNIX
132     // FIXME: move getpid() call into LLVM
133     char hostname[256];
134     hostname[255] = 0;
135     hostname[0] = 0;
136     gethostname(hostname, 255);
137     Out << hostname << ' ' << getpid();
138 #else
139     Out << "localhost 1";
140 #endif
141     Out.close();
142 
143     if (Out.has_error()) {
144       // We failed to write out PID, so make up an excuse, remove the
145       // unique lock file, and fail.
146       Error = make_error_code(errc::no_space_on_device);
147       sys::fs::remove(UniqueLockFileName);
148       return;
149     }
150   }
151 
152   // Clean up the unique file on signal, which also releases the lock if it is
153   // held since the .lock symlink will point to a nonexistent file.
154   RemoveUniqueLockFileOnSignal RemoveUniqueFile(UniqueLockFileName);
155 
156   while (1) {
157     // Create a link from the lock file name. If this succeeds, we're done.
158     std::error_code EC =
159         sys::fs::create_link(UniqueLockFileName, LockFileName);
160     if (!EC) {
161       RemoveUniqueFile.lockAcquired();
162       return;
163     }
164 
165     if (EC != errc::file_exists) {
166       Error = EC;
167       return;
168     }
169 
170     // Someone else managed to create the lock file first. Read the process ID
171     // from the lock file.
172     if ((Owner = readLockFile(LockFileName))) {
173       // Wipe out our unique lock file (it's useless now)
174       sys::fs::remove(UniqueLockFileName);
175       return;
176     }
177 
178     if (!sys::fs::exists(LockFileName)) {
179       // The previous owner released the lock file before we could read it.
180       // Try to get ownership again.
181       continue;
182     }
183 
184     // There is a lock file that nobody owns; try to clean it up and get
185     // ownership.
186     if ((EC = sys::fs::remove(LockFileName))) {
187       Error = EC;
188       return;
189     }
190   }
191 }
192 
193 LockFileManager::LockFileState LockFileManager::getState() const {
194   if (Owner)
195     return LFS_Shared;
196 
197   if (Error)
198     return LFS_Error;
199 
200   return LFS_Owned;
201 }
202 
203 LockFileManager::~LockFileManager() {
204   if (getState() != LFS_Owned)
205     return;
206 
207   // Since we own the lock, remove the lock file and our own unique lock file.
208   sys::fs::remove(LockFileName);
209   sys::fs::remove(UniqueLockFileName);
210   // The unique file is now gone, so remove it from the signal handler. This
211   // matches a sys::RemoveFileOnSignal() in LockFileManager().
212   sys::DontRemoveFileOnSignal(UniqueLockFileName);
213 }
214 
215 LockFileManager::WaitForUnlockResult LockFileManager::waitForUnlock() {
216   if (getState() != LFS_Shared)
217     return Res_Success;
218 
219 #if LLVM_ON_WIN32
220   unsigned long Interval = 1;
221 #else
222   struct timespec Interval;
223   Interval.tv_sec = 0;
224   Interval.tv_nsec = 1000000;
225 #endif
226   // Don't wait more than five minutes per iteration. Total timeout for the file
227   // to appear is ~8.5 mins.
228   const unsigned MaxSeconds = 5*60;
229   do {
230     // Sleep for the designated interval, to allow the owning process time to
231     // finish up and remove the lock file.
232     // FIXME: Should we hook in to system APIs to get a notification when the
233     // lock file is deleted?
234 #if LLVM_ON_WIN32
235     Sleep(Interval);
236 #else
237     nanosleep(&Interval, nullptr);
238 #endif
239 
240     if (sys::fs::access(LockFileName.c_str(), sys::fs::AccessMode::Exist) ==
241         errc::no_such_file_or_directory) {
242       // If the original file wasn't created, somone thought the lock was dead.
243       if (!sys::fs::exists(FileName))
244         return Res_OwnerDied;
245       return Res_Success;
246     }
247 
248     // If the process owning the lock died without cleaning up, just bail out.
249     if (!processStillExecuting((*Owner).first, (*Owner).second))
250       return Res_OwnerDied;
251 
252     // Exponentially increase the time we wait for the lock to be removed.
253 #if LLVM_ON_WIN32
254     Interval *= 2;
255 #else
256     Interval.tv_sec *= 2;
257     Interval.tv_nsec *= 2;
258     if (Interval.tv_nsec >= 1000000000) {
259       ++Interval.tv_sec;
260       Interval.tv_nsec -= 1000000000;
261     }
262 #endif
263   } while (
264 #if LLVM_ON_WIN32
265            Interval < MaxSeconds * 1000
266 #else
267            Interval.tv_sec < (time_t)MaxSeconds
268 #endif
269            );
270 
271   // Give up.
272   return Res_Timeout;
273 }
274 
275 std::error_code LockFileManager::unsafeRemoveLockFile() {
276   return sys::fs::remove(LockFileName);
277 }
278