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      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/FileSystem.h"
     13 #include "llvm/Support/MemoryBuffer.h"
     14 #include "llvm/Support/raw_ostream.h"
     15 #include <sys/stat.h>
     16 #include <sys/types.h>
     17 #if LLVM_ON_WIN32
     18 #include <windows.h>
     19 #endif
     20 #if LLVM_ON_UNIX
     21 #include <unistd.h>
     22 #endif
     23 using namespace llvm;
     24 
     25 /// \brief Attempt to read the lock file with the given name, if it exists.
     26 ///
     27 /// \param LockFileName The name of the lock file to read.
     28 ///
     29 /// \returns The process ID of the process that owns this lock file
     30 Optional<std::pair<std::string, int> >
     31 LockFileManager::readLockFile(StringRef LockFileName) {
     32   // Check whether the lock file exists. If not, clearly there's nothing
     33   // to read, so we just return.
     34   bool Exists = false;
     35   if (sys::fs::exists(LockFileName, Exists) || !Exists)
     36     return None;
     37 
     38   // Read the owning host and PID out of the lock file. If it appears that the
     39   // owning process is dead, the lock file is invalid.
     40   OwningPtr<MemoryBuffer> MB;
     41   if (MemoryBuffer::getFile(LockFileName, MB))
     42     return None;
     43 
     44   StringRef Hostname;
     45   StringRef PIDStr;
     46   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     return std::make_pair(std::string(Hostname), PID);
     51 
     52   // Delete the lock file. It's invalid anyway.
     53   sys::fs::remove(LockFileName);
     54   return None;
     55 }
     56 
     57 bool LockFileManager::processStillExecuting(StringRef Hostname, int PID) {
     58 #if LLVM_ON_UNIX && !defined(__ANDROID__)
     59   char MyHostname[256];
     60   MyHostname[255] = 0;
     61   MyHostname[0] = 0;
     62   gethostname(MyHostname, 255);
     63   // Check whether the process is dead. If so, we're done.
     64   if (MyHostname == Hostname && getsid(PID) == -1 && errno == ESRCH)
     65     return false;
     66 #endif
     67 
     68   return true;
     69 }
     70 
     71 LockFileManager::LockFileManager(StringRef FileName)
     72 {
     73   this->FileName = FileName;
     74   LockFileName = FileName;
     75   LockFileName += ".lock";
     76 
     77   // If the lock file already exists, don't bother to try to create our own
     78   // lock file; it won't work anyway. Just figure out who owns this lock file.
     79   if ((Owner = readLockFile(LockFileName)))
     80     return;
     81 
     82   // Create a lock file that is unique to this instance.
     83   UniqueLockFileName = LockFileName;
     84   UniqueLockFileName += "-%%%%%%%%";
     85   int UniqueLockFileID;
     86   if (error_code EC
     87         = sys::fs::createUniqueFile(UniqueLockFileName.str(),
     88                                     UniqueLockFileID,
     89                                     UniqueLockFileName)) {
     90     Error = EC;
     91     return;
     92   }
     93 
     94   // Write our process ID to our unique lock file.
     95   {
     96     raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
     97 
     98 #if LLVM_ON_UNIX
     99     // FIXME: move getpid() call into LLVM
    100     char hostname[256];
    101     hostname[255] = 0;
    102     hostname[0] = 0;
    103     gethostname(hostname, 255);
    104     Out << hostname << ' ' << getpid();
    105 #else
    106     Out << "localhost 1";
    107 #endif
    108     Out.close();
    109 
    110     if (Out.has_error()) {
    111       // We failed to write out PID, so make up an excuse, remove the
    112       // unique lock file, and fail.
    113       Error = make_error_code(errc::no_space_on_device);
    114       bool Existed;
    115       sys::fs::remove(UniqueLockFileName.c_str(), Existed);
    116       return;
    117     }
    118   }
    119 
    120   // Create a hard link from the lock file name. If this succeeds, we're done.
    121   error_code EC
    122     = sys::fs::create_hard_link(UniqueLockFileName.str(),
    123                                       LockFileName.str());
    124   if (EC == errc::success)
    125     return;
    126 
    127   // Creating the hard link failed.
    128 
    129 #ifdef LLVM_ON_UNIX
    130   // The creation of the hard link may appear to fail, but if stat'ing the
    131   // unique file returns a link count of 2, then we can still declare success.
    132   struct stat StatBuf;
    133   if (stat(UniqueLockFileName.c_str(), &StatBuf) == 0 &&
    134       StatBuf.st_nlink == 2)
    135     return;
    136 #endif
    137 
    138   // Someone else managed to create the lock file first. Wipe out our unique
    139   // lock file (it's useless now) and read the process ID from the lock file.
    140   bool Existed;
    141   sys::fs::remove(UniqueLockFileName.str(), Existed);
    142   if ((Owner = readLockFile(LockFileName)))
    143     return;
    144 
    145   // There is a lock file that nobody owns; try to clean it up and report
    146   // an error.
    147   sys::fs::remove(LockFileName.str(), Existed);
    148   Error = EC;
    149 }
    150 
    151 LockFileManager::LockFileState LockFileManager::getState() const {
    152   if (Owner)
    153     return LFS_Shared;
    154 
    155   if (Error)
    156     return LFS_Error;
    157 
    158   return LFS_Owned;
    159 }
    160 
    161 LockFileManager::~LockFileManager() {
    162   if (getState() != LFS_Owned)
    163     return;
    164 
    165   // Since we own the lock, remove the lock file and our own unique lock file.
    166   bool Existed;
    167   sys::fs::remove(LockFileName.str(), Existed);
    168   sys::fs::remove(UniqueLockFileName.str(), Existed);
    169 }
    170 
    171 void LockFileManager::waitForUnlock() {
    172   if (getState() != LFS_Shared)
    173     return;
    174 
    175 #if LLVM_ON_WIN32
    176   unsigned long Interval = 1;
    177 #else
    178   struct timespec Interval;
    179   Interval.tv_sec = 0;
    180   Interval.tv_nsec = 1000000;
    181 #endif
    182   // Don't wait more than five minutes for the file to appear.
    183   unsigned MaxSeconds = 300;
    184   bool LockFileGone = false;
    185   do {
    186     // Sleep for the designated interval, to allow the owning process time to
    187     // finish up and remove the lock file.
    188     // FIXME: Should we hook in to system APIs to get a notification when the
    189     // lock file is deleted?
    190 #if LLVM_ON_WIN32
    191     Sleep(Interval);
    192 #else
    193     nanosleep(&Interval, NULL);
    194 #endif
    195     bool Exists = false;
    196     bool LockFileJustDisappeared = false;
    197 
    198     // If the lock file is still expected to be there, check whether it still
    199     // is.
    200     if (!LockFileGone) {
    201       if (!sys::fs::exists(LockFileName.str(), Exists) && !Exists) {
    202         LockFileGone = true;
    203         LockFileJustDisappeared = true;
    204         Exists = false;
    205       }
    206     }
    207 
    208     // If the lock file is no longer there, check if the original file is
    209     // available now.
    210     if (LockFileGone) {
    211       if (!sys::fs::exists(FileName.str(), Exists) && Exists) {
    212         return;
    213       }
    214 
    215       // The lock file is gone, so now we're waiting for the original file to
    216       // show up. If this just happened, reset our waiting intervals and keep
    217       // waiting.
    218       if (LockFileJustDisappeared) {
    219         MaxSeconds = 5;
    220 
    221 #if LLVM_ON_WIN32
    222         Interval = 1;
    223 #else
    224         Interval.tv_sec = 0;
    225         Interval.tv_nsec = 1000000;
    226 #endif
    227         continue;
    228       }
    229     }
    230 
    231     // If we're looking for the lock file to disappear, but the process
    232     // owning the lock died without cleaning up, just bail out.
    233     if (!LockFileGone &&
    234         !processStillExecuting((*Owner).first, (*Owner).second)) {
    235       return;
    236     }
    237 
    238     // Exponentially increase the time we wait for the lock to be removed.
    239 #if LLVM_ON_WIN32
    240     Interval *= 2;
    241 #else
    242     Interval.tv_sec *= 2;
    243     Interval.tv_nsec *= 2;
    244     if (Interval.tv_nsec >= 1000000000) {
    245       ++Interval.tv_sec;
    246       Interval.tv_nsec -= 1000000000;
    247     }
    248 #endif
    249   } while (
    250 #if LLVM_ON_WIN32
    251            Interval < MaxSeconds * 1000
    252 #else
    253            Interval.tv_sec < (time_t)MaxSeconds
    254 #endif
    255            );
    256 
    257   // Give up.
    258 }
    259