xref: /freebsd/contrib/llvm-project/llvm/lib/Support/LockFileManager.cpp (revision 06e20d1babecec1f45ffda513f55a8db5f1c0f56)
1 //===--- LockFileManager.cpp - File-level Locking Utility------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "llvm/Support/LockFileManager.h"
10 #include "llvm/ADT/None.h"
11 #include "llvm/ADT/SmallVector.h"
12 #include "llvm/ADT/StringExtras.h"
13 #include "llvm/Support/Errc.h"
14 #include "llvm/Support/ErrorOr.h"
15 #include "llvm/Support/FileSystem.h"
16 #include "llvm/Support/MemoryBuffer.h"
17 #include "llvm/Support/Process.h"
18 #include "llvm/Support/Signals.h"
19 #include "llvm/Support/raw_ostream.h"
20 #include <cerrno>
21 #include <chrono>
22 #include <ctime>
23 #include <memory>
24 #include <random>
25 #include <sys/stat.h>
26 #include <sys/types.h>
27 #include <system_error>
28 #include <thread>
29 #include <tuple>
30 
31 #ifdef _WIN32
32 #include <windows.h>
33 #endif
34 #if LLVM_ON_UNIX
35 #include <unistd.h>
36 #endif
37 
38 #if defined(__APPLE__) && defined(__MAC_OS_X_VERSION_MIN_REQUIRED) && (__MAC_OS_X_VERSION_MIN_REQUIRED > 1050)
39 #define USE_OSX_GETHOSTUUID 1
40 #else
41 #define USE_OSX_GETHOSTUUID 0
42 #endif
43 
44 #if USE_OSX_GETHOSTUUID
45 #include <uuid/uuid.h>
46 #endif
47 
48 using namespace llvm;
49 
50 /// Attempt to read the lock file with the given name, if it exists.
51 ///
52 /// \param LockFileName The name of the lock file to read.
53 ///
54 /// \returns The process ID of the process that owns this lock file
55 Optional<std::pair<std::string, int> >
56 LockFileManager::readLockFile(StringRef LockFileName) {
57   // Read the owning host and PID out of the lock file. If it appears that the
58   // owning process is dead, the lock file is invalid.
59   ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
60       MemoryBuffer::getFile(LockFileName);
61   if (!MBOrErr) {
62     sys::fs::remove(LockFileName);
63     return None;
64   }
65   MemoryBuffer &MB = *MBOrErr.get();
66 
67   StringRef Hostname;
68   StringRef PIDStr;
69   std::tie(Hostname, PIDStr) = getToken(MB.getBuffer(), " ");
70   PIDStr = PIDStr.substr(PIDStr.find_first_not_of(" "));
71   int PID;
72   if (!PIDStr.getAsInteger(10, PID)) {
73     auto Owner = std::make_pair(std::string(Hostname), PID);
74     if (processStillExecuting(Owner.first, Owner.second))
75       return Owner;
76   }
77 
78   // Delete the lock file. It's invalid anyway.
79   sys::fs::remove(LockFileName);
80   return None;
81 }
82 
83 static std::error_code getHostID(SmallVectorImpl<char> &HostID) {
84   HostID.clear();
85 
86 #if USE_OSX_GETHOSTUUID
87   // On OS X, use the more stable hardware UUID instead of hostname.
88   struct timespec wait = {1, 0}; // 1 second.
89   uuid_t uuid;
90   if (gethostuuid(uuid, &wait) != 0)
91     return std::error_code(errno, std::system_category());
92 
93   uuid_string_t UUIDStr;
94   uuid_unparse(uuid, UUIDStr);
95   StringRef UUIDRef(UUIDStr);
96   HostID.append(UUIDRef.begin(), UUIDRef.end());
97 
98 #elif LLVM_ON_UNIX
99   char HostName[256];
100   HostName[255] = 0;
101   HostName[0] = 0;
102   gethostname(HostName, 255);
103   StringRef HostNameRef(HostName);
104   HostID.append(HostNameRef.begin(), HostNameRef.end());
105 
106 #else
107   StringRef Dummy("localhost");
108   HostID.append(Dummy.begin(), Dummy.end());
109 #endif
110 
111   return std::error_code();
112 }
113 
114 bool LockFileManager::processStillExecuting(StringRef HostID, int PID) {
115 #if LLVM_ON_UNIX && !defined(__ANDROID__)
116   SmallString<256> StoredHostID;
117   if (getHostID(StoredHostID))
118     return true; // Conservatively assume it's executing on error.
119 
120   // Check whether the process is dead. If so, we're done.
121   if (StoredHostID == HostID && getsid(PID) == -1 && errno == ESRCH)
122     return false;
123 #endif
124 
125   return true;
126 }
127 
128 namespace {
129 
130 /// An RAII helper object ensure that the unique lock file is removed.
131 ///
132 /// Ensures that if there is an error or a signal before we finish acquiring the
133 /// lock, the unique file will be removed. And if we successfully take the lock,
134 /// the signal handler is left in place so that signals while the lock is held
135 /// will remove the unique lock file. The caller should ensure there is a
136 /// matching call to sys::DontRemoveFileOnSignal when the lock is released.
137 class RemoveUniqueLockFileOnSignal {
138   StringRef Filename;
139   bool RemoveImmediately;
140 public:
141   RemoveUniqueLockFileOnSignal(StringRef Name)
142   : Filename(Name), RemoveImmediately(true) {
143     sys::RemoveFileOnSignal(Filename, nullptr);
144   }
145 
146   ~RemoveUniqueLockFileOnSignal() {
147     if (!RemoveImmediately) {
148       // Leave the signal handler enabled. It will be removed when the lock is
149       // released.
150       return;
151     }
152     sys::fs::remove(Filename);
153     sys::DontRemoveFileOnSignal(Filename);
154   }
155 
156   void lockAcquired() { RemoveImmediately = false; }
157 };
158 
159 } // end anonymous namespace
160 
161 LockFileManager::LockFileManager(StringRef FileName)
162 {
163   this->FileName = FileName;
164   if (std::error_code EC = sys::fs::make_absolute(this->FileName)) {
165     std::string S("failed to obtain absolute path for ");
166     S.append(std::string(this->FileName.str()));
167     setError(EC, S);
168     return;
169   }
170   LockFileName = this->FileName;
171   LockFileName += ".lock";
172 
173   // If the lock file already exists, don't bother to try to create our own
174   // lock file; it won't work anyway. Just figure out who owns this lock file.
175   if ((Owner = readLockFile(LockFileName)))
176     return;
177 
178   // Create a lock file that is unique to this instance.
179   UniqueLockFileName = LockFileName;
180   UniqueLockFileName += "-%%%%%%%%";
181   int UniqueLockFileID;
182   if (std::error_code EC = sys::fs::createUniqueFile(
183           UniqueLockFileName, UniqueLockFileID, UniqueLockFileName)) {
184     std::string S("failed to create unique file ");
185     S.append(std::string(UniqueLockFileName.str()));
186     setError(EC, S);
187     return;
188   }
189 
190   // Write our process ID to our unique lock file.
191   {
192     SmallString<256> HostID;
193     if (auto EC = getHostID(HostID)) {
194       setError(EC, "failed to get host id");
195       return;
196     }
197 
198     raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
199     Out << HostID << ' ' << sys::Process::getProcessId();
200     Out.close();
201 
202     if (Out.has_error()) {
203       // We failed to write out PID, so report the error, remove the
204       // unique lock file, and fail.
205       std::string S("failed to write to ");
206       S.append(std::string(UniqueLockFileName.str()));
207       setError(Out.error(), S);
208       sys::fs::remove(UniqueLockFileName);
209       return;
210     }
211   }
212 
213   // Clean up the unique file on signal, which also releases the lock if it is
214   // held since the .lock symlink will point to a nonexistent file.
215   RemoveUniqueLockFileOnSignal RemoveUniqueFile(UniqueLockFileName);
216 
217   while (true) {
218     // Create a link from the lock file name. If this succeeds, we're done.
219     std::error_code EC =
220         sys::fs::create_link(UniqueLockFileName, LockFileName);
221     if (!EC) {
222       RemoveUniqueFile.lockAcquired();
223       return;
224     }
225 
226     if (EC != errc::file_exists) {
227       std::string S("failed to create link ");
228       raw_string_ostream OSS(S);
229       OSS << LockFileName.str() << " to " << UniqueLockFileName.str();
230       setError(EC, OSS.str());
231       return;
232     }
233 
234     // Someone else managed to create the lock file first. Read the process ID
235     // from the lock file.
236     if ((Owner = readLockFile(LockFileName))) {
237       // Wipe out our unique lock file (it's useless now)
238       sys::fs::remove(UniqueLockFileName);
239       return;
240     }
241 
242     if (!sys::fs::exists(LockFileName)) {
243       // The previous owner released the lock file before we could read it.
244       // Try to get ownership again.
245       continue;
246     }
247 
248     // There is a lock file that nobody owns; try to clean it up and get
249     // ownership.
250     if ((EC = sys::fs::remove(LockFileName))) {
251       std::string S("failed to remove lockfile ");
252       S.append(std::string(UniqueLockFileName.str()));
253       setError(EC, S);
254       return;
255     }
256   }
257 }
258 
259 LockFileManager::LockFileState LockFileManager::getState() const {
260   if (Owner)
261     return LFS_Shared;
262 
263   if (ErrorCode)
264     return LFS_Error;
265 
266   return LFS_Owned;
267 }
268 
269 std::string LockFileManager::getErrorMessage() const {
270   if (ErrorCode) {
271     std::string Str(ErrorDiagMsg);
272     std::string ErrCodeMsg = ErrorCode.message();
273     raw_string_ostream OSS(Str);
274     if (!ErrCodeMsg.empty())
275       OSS << ": " << ErrCodeMsg;
276     return OSS.str();
277   }
278   return "";
279 }
280 
281 LockFileManager::~LockFileManager() {
282   if (getState() != LFS_Owned)
283     return;
284 
285   // Since we own the lock, remove the lock file and our own unique lock file.
286   sys::fs::remove(LockFileName);
287   sys::fs::remove(UniqueLockFileName);
288   // The unique file is now gone, so remove it from the signal handler. This
289   // matches a sys::RemoveFileOnSignal() in LockFileManager().
290   sys::DontRemoveFileOnSignal(UniqueLockFileName);
291 }
292 
293 LockFileManager::WaitForUnlockResult
294 LockFileManager::waitForUnlock(const unsigned MaxSeconds) {
295   if (getState() != LFS_Shared)
296     return Res_Success;
297 
298   // Since we don't yet have an event-based method to wait for the lock file,
299   // implement randomized exponential backoff, similar to Ethernet collision
300   // algorithm. This improves performance on machines with high core counts
301   // when the file lock is heavily contended by multiple clang processes
302   const unsigned long MinWaitDurationMS = 10;
303   const unsigned long MaxWaitMultiplier = 50; // 500ms max wait
304   unsigned long WaitMultiplier = 1;
305   unsigned long ElapsedTimeSeconds = 0;
306 
307   std::random_device Device;
308   std::default_random_engine Engine(Device());
309 
310   auto StartTime = std::chrono::steady_clock::now();
311 
312   do {
313     // FIXME: implement event-based waiting
314 
315     // Sleep for the designated interval, to allow the owning process time to
316     // finish up and remove the lock file.
317     std::uniform_int_distribution<unsigned long> Distribution(1,
318                                                               WaitMultiplier);
319     unsigned long WaitDurationMS = MinWaitDurationMS * Distribution(Engine);
320     std::this_thread::sleep_for(std::chrono::milliseconds(WaitDurationMS));
321 
322     if (sys::fs::access(LockFileName.c_str(), sys::fs::AccessMode::Exist) ==
323         errc::no_such_file_or_directory) {
324       // If the original file wasn't created, somone thought the lock was dead.
325       if (!sys::fs::exists(FileName))
326         return Res_OwnerDied;
327       return Res_Success;
328     }
329 
330     // If the process owning the lock died without cleaning up, just bail out.
331     if (!processStillExecuting((*Owner).first, (*Owner).second))
332       return Res_OwnerDied;
333 
334     WaitMultiplier *= 2;
335     if (WaitMultiplier > MaxWaitMultiplier) {
336       WaitMultiplier = MaxWaitMultiplier;
337     }
338 
339     ElapsedTimeSeconds = std::chrono::duration_cast<std::chrono::seconds>(
340                              std::chrono::steady_clock::now() - StartTime)
341                              .count();
342 
343   } while (ElapsedTimeSeconds < MaxSeconds);
344 
345   // Give up.
346   return Res_Timeout;
347 }
348 
349 std::error_code LockFileManager::unsafeRemoveLockFile() {
350   return sys::fs::remove(LockFileName);
351 }
352