Example code

examples/socket_grid.cc

@@ -0,0 +1,133 @@
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <err.h>
+#include <fcntl.h>
+#include <assert.h>
+#include <string.h>
+#include <stdlib.h>
+
+static int sock;
+static const char *sock_path_fmt = "/tmp/GridUnixSocket.%d";
+static char sock_path[256];
+
+class UnixSockets {
+public:
+  static void Open(int rank)
+  {
+    int errnum;
+
+    sock = socket(AF_UNIX, SOCK_DGRAM, 0);  assert(sock>0);
+    printf("allocated socket %d\n",sock);
+
+    struct sockaddr_un sa_un = { 0 };
+    sa_un.sun_family = AF_UNIX;
+    snprintf(sa_un.sun_path, sizeof(sa_un.sun_path),sock_path_fmt,rank);
+    unlink(sa_un.sun_path);
+    if (bind(sock, (struct sockaddr *)&sa_un, sizeof(sa_un))) {
+      perror("bind failure");
+      exit(EXIT_FAILURE);
+    }
+    printf("bound socket %d to %s\n",sock,sa_un.sun_path);
+  }
+
+  static int RecvFileDescriptor(void)
+  {
+    int n;
+    int fd;
+    char buf[1];
+    struct iovec iov;
+    struct msghdr msg;
+    struct cmsghdr *cmsg;
+    char cms[CMSG_SPACE(sizeof(int))];
+
+    iov.iov_base = buf;
+    iov.iov_len = 1;
+
+    memset(&msg, 0, sizeof msg);
+    msg.msg_name = 0;
+    msg.msg_namelen = 0;
+    msg.msg_iov = &iov;
+    msg.msg_iovlen = 1;
+
+    msg.msg_control = (caddr_t)cms;
+    msg.msg_controllen = sizeof cms;
+
+    if((n=recvmsg(sock, &msg, 0)) < 0) {
+      perror("recvmsg failed");
+      return -1;
+    }
+    if(n == 0){
+      perror("recvmsg returned 0");
+      return -1;
+    }
+    cmsg = CMSG_FIRSTHDR(&msg);
+    memmove(&fd, CMSG_DATA(cmsg), sizeof(int));
+    printf("received fd %d from socket %d\n",fd,sock);
+    return fd;
+  }
+
+  static void SendFileDescriptor(int fildes,int xmit_to_rank)
+  {
+    struct msghdr msg;
+    struct iovec iov;
+    struct cmsghdr *cmsg = NULL;
+    char ctrl[CMSG_SPACE(sizeof(int))];
+    char data = ' ';
+
+    memset(&msg, 0, sizeof(struct msghdr));
+    memset(ctrl, 0, CMSG_SPACE(sizeof(int)));
+    iov.iov_base = &data;
+    iov.iov_len = sizeof(data);
+    
+    sprintf(sock_path,sock_path_fmt,xmit_to_rank);
+    printf("sending FD %d over socket %d to rank %d AF_UNIX path %s\n",fildes,sock,xmit_to_rank,sock_path);fflush(stdout);
+    
+    struct sockaddr_un sa_un = { 0 };
+    sa_un.sun_family = AF_UNIX;
+    snprintf(sa_un.sun_path, sizeof(sa_un.sun_path),sock_path_fmt,xmit_to_rank);
+
+    msg.msg_name = (void *)&sa_un;
+    msg.msg_namelen = sizeof(sa_un);
+    msg.msg_iov = &iov;
+    msg.msg_iovlen = 1;
+    msg.msg_controllen =  CMSG_SPACE(sizeof(int));
+    msg.msg_control = ctrl;
+
+    cmsg = CMSG_FIRSTHDR(&msg);
+    cmsg->cmsg_level = SOL_SOCKET;
+    cmsg->cmsg_type = SCM_RIGHTS;
+    cmsg->cmsg_len = CMSG_LEN(sizeof(int));
+
+    *((int *) CMSG_DATA(cmsg)) = fildes;
+
+    if ( sendmsg(sock, &msg, 0) == -1 ) perror("sendmsg failed");
+  };
+};
+
+int main(int argc, char **argv)
+{
+  int me = fork()?0:1;
+  
+  UnixSockets::Open(me);
+  
+  // need MPI barrier
+  sleep(10);
+  const char * message = "Hello, World\n";
+  if( me ) {
+    int fd = open("foo",O_RDWR|O_CREAT,0666);
+    if ( fd < 0 ) {
+      perror("failed to open file");
+      exit(EXIT_FAILURE);
+    }
+    // rank 1 sends ot rank 0
+    UnixSockets::SendFileDescriptor(fd,0);
+    close(fd);
+  } else {
+    // rank 0 sends receives frmo rank 1
+    int fd = UnixSockets::RecvFileDescriptor();
+    write(fd,(const void *)message,strlen(message));
+    close(fd);
+  }
+}