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  1. #include <string>
  2. #include <stdexcept>
  3. #include <iostream>
  4. #include <cassert>
  5. #include <thread>
  6. #include <chrono>
  7.  
  8. #include <cstdlib>
  9. #include <unistd.h>
  10. #include <sys/file.h>
  11. #include <sys/stat.h>
  12.  
  13. struct FileLock
  14.   {
  15.   std::string _path;
  16.  
  17.   FileLock(const std::string& p, bool acq = false)
  18.     : _path(p)
  19.     {
  20.     if (acq)
  21.       {
  22.       bool r = acquire();
  23.       if (!r) throw std::runtime_error("FileLock::acquire failed");
  24.       }
  25.     }
  26.  
  27.   ~FileLock()
  28.     {
  29.     bool r = release();
  30.     if (!r) std::cerr << "FileLock::release failed";
  31.     }
  32.  
  33.   const char* path() const {return _path.c_str();}
  34.  
  35.   // #############################################################################
  36.  
  37. #define CHECK_OK_(v, pred)                                \
  38.   {                                                       \
  39.   bool res = (pred);                                        \
  40.   if (!res) std::cerr<< ("FileLock: (" #pred ") = false");   \
  41.   v &= res;                                                 \
  42.   }
  43.  
  44.   bool acquire()
  45.     {
  46.     bool ok = true;
  47.     int r;
  48.  
  49.     // auto fp = std::fopen(_path.c_str(), "w");
  50.     // if (!fp)
  51.     //   return false;
  52.  
  53.     // int fd = ::fileno(fp);
  54.  
  55.     auto m = umask(0);
  56.     int fd = ::open(_path.c_str(), O_RDWR | O_CREAT, 0666);
  57.     umask(m);
  58.  
  59.     CHECK_OK_(ok, fd != -1);
  60.     if (ok)
  61.       {
  62.       r = ::flock(fd, LOCK_EX | LOCK_NB);
  63.       CHECK_OK_(ok, r != -1);
  64.       if (ok)
  65.         {                       // write pid
  66.         pid_t pid = getpid();
  67.         auto pstr = std::to_string(pid);
  68.         auto wr = ::write(fd, pstr.c_str(), pstr.size());
  69.         CHECK_OK_(ok, wr == pstr.size());
  70.         }
  71.       }
  72.  
  73.     // CHECK_OK_(ok,  std::fclose(fp) == 0);
  74.     CHECK_OK_(ok, ::close(fd) == 0);
  75.  
  76.     return ok;
  77.     }
  78.  
  79.   // #############################################################################
  80.  
  81.   bool release()
  82.     {
  83.     bool ok = true;
  84.  
  85.     // auto fp = std::fopen(_path.c_str(), "r");
  86.     // if (!fp)
  87.     //   return false;
  88.  
  89.     // int fd = ::fileno(fp);
  90.  
  91.     int fd = ::open(_path.c_str(), O_RDONLY);
  92.     CHECK_OK_(ok, fd != -1);
  93.     if (ok)
  94.       {
  95.       int r = ::flock(fd, LOCK_UN | LOCK_NB);
  96.       CHECK_OK_(ok, r != -1);
  97.       }
  98.  
  99.     // pid should == getpid()
  100.  
  101.     // CHECK_OK_(ok, std::fclose(fp) == 0);
  102.     CHECK_OK_(ok, ::close(fd) == 0);
  103.  
  104.     // necessary?
  105.     CHECK_OK_(ok, std::remove(_path.c_str()) != -1);
  106.  
  107.     return ok;
  108.     }
  109.  
  110. #undef CHECK_OK_
  111.  
  112.   };
  113.  
  114. int main(int ac, const char* av[])
  115. {
  116.   assert((ac >= 2) && "usage: prog file_name");
  117.  
  118.   FileLock fl(av[1], true);
  119.  
  120.   while (1)
  121.   {
  122.     std::this_thread::sleep_for(std::chrono::seconds{1});
  123.     std::cout << "waiting... \n";
  124.   }
  125. }
  126.  
Runtime error #stdin #stdout #stderr 0s 3432KB
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Standard input is empty
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Standard output is empty
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prog: prog.cpp:116: int main(int, const char**): Assertion `(ac >= 2) && "usage: prog file_name"' failed.
https://ideone.com/K00Suw
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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