带IPC_EXCL的shmget

Question

./test 10 0
./test 10 1

谢谢你的帮助！

#include <sys/shm.h>
#include <sys/stat.h>
#include <errno.h>

#include <stdlib.h>
#include <vector>
#include <iostream>
#include <stdexcept>
using namespace std;

int main( int argc, char** argv )
{
   cout << "usage: " << argv[0] << " <key> <mode (0=creator 1=client)>" << endl;
   if ( argc < 3 ) return 0;

   int key  = atoi( argv[1] );
   int mode = atoi( argv[2] );

   cout << "key=" << key << endl;
   cout << "mode=" << mode << endl;

   char c;
   int shmid=-1;
   int size = 100; // bytes

   try
   {
      if ( mode == 0 ) // creator
      {
         cout << "creating segment" << endl;
         int flags = ( IPC_CREAT | IPC_EXCL | 0666 );
         shmid = shmget( key, size, flags );

         if ( shmid== -1 )
            throw runtime_error("failed to create segment");

         cout << "created: shmid=" << shmid << endl;
      }
      else if ( mode == 1 )
      {
         shmid = shmget( key, 0, 0 );

         if ( shmid== -1 )
            throw runtime_error("failed to load");

         cout << "loaded: shmid=" << shmid << endl;
      }

      cout << "attach? (press key to continue)" << endl;
      cin >> c;

      void* data = shmat( shmid, NULL, 0 );

      if ( data == (void *) -1 )
         throw runtime_error("failed to attach");

      cout << "attached to id=" << shmid << endl;

      cout << "destroy? (press key to continue)" << endl;
      cin >> c;

      if ( shmctl( shmid, IPC_RMID, NULL ) == -1 )
         throw runtime_error("failed to destroy");

      cout << "destroyed" << endl;
   }
   catch( const exception& e )
   {
      cout << e.what() << " errno=" << errno << endl;
   }
}

Answer 1

您应该更加关注IPCS的输出。使用带有10键的示例代码。

服务器已经创建了段：

$ ipcs -m
------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x0000000a 1470791680 hristo     666        100        1

客户端已连接，服务器已将段标记为要销毁：

$ ipcs -m
------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 1470791680 hristo     666        100        1          dest
^^^^^^^^^^