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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/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   std::unique_ptr<MemoryBuffer> MB = std::move(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 five minutes for the file to appear.
    190   unsigned MaxSeconds = 300;
    191   bool LockFileGone = false;
    192   do {
    193     // Sleep for the designated interval, to allow the owning process time to
    194     // finish up and remove the lock file.
    195     // FIXME: Should we hook in to system APIs to get a notification when the
    196     // lock file is deleted?
    197 #if LLVM_ON_WIN32
    198     Sleep(Interval);
    199 #else
    200     nanosleep(&Interval, nullptr);
    201 #endif
    202     bool LockFileJustDisappeared = false;
    203 
    204     // If the lock file is still expected to be there, check whether it still
    205     // is.
    206     if (!LockFileGone) {
    207       bool Exists;
    208       if (!sys::fs::exists(LockFileName.str(), Exists) && !Exists) {
    209         LockFileGone = true;
    210         LockFileJustDisappeared = true;
    211       }
    212     }
    213 
    214     // If the lock file is no longer there, check if the original file is
    215     // available now.
    216     if (LockFileGone) {
    217       if (sys::fs::exists(FileName.str())) {
    218         return Res_Success;
    219       }
    220 
    221       // The lock file is gone, so now we're waiting for the original file to
    222       // show up. If this just happened, reset our waiting intervals and keep
    223       // waiting.
    224       if (LockFileJustDisappeared) {
    225         MaxSeconds = 5;
    226 
    227 #if LLVM_ON_WIN32
    228         Interval = 1;
    229 #else
    230         Interval.tv_sec = 0;
    231         Interval.tv_nsec = 1000000;
    232 #endif
    233         continue;
    234       }
    235     }
    236 
    237     // If we're looking for the lock file to disappear, but the process
    238     // owning the lock died without cleaning up, just bail out.
    239     if (!LockFileGone &&
    240         !processStillExecuting((*Owner).first, (*Owner).second)) {
    241       return Res_OwnerDied;
    242     }
    243 
    244     // Exponentially increase the time we wait for the lock to be removed.
    245 #if LLVM_ON_WIN32
    246     Interval *= 2;
    247 #else
    248     Interval.tv_sec *= 2;
    249     Interval.tv_nsec *= 2;
    250     if (Interval.tv_nsec >= 1000000000) {
    251       ++Interval.tv_sec;
    252       Interval.tv_nsec -= 1000000000;
    253     }
    254 #endif
    255   } while (
    256 #if LLVM_ON_WIN32
    257            Interval < MaxSeconds * 1000
    258 #else
    259            Interval.tv_sec < (time_t)MaxSeconds
    260 #endif
    261            );
    262 
    263   // Give up.
    264   return Res_Timeout;
    265 }
    266