/**************************************************************** * * * LIBDIST V1.0 * * * * elec.c -- election algorithm * * * * Last changed: 19.02.96 * * Author: Frank Kargl (frank.kargl@informatik.uni-ulm.de) * * * * Restrictions: works only for Solaris 2.6 or above * * * ****************************************************************/ #include "libdist.h" #include "config.h" #include /* for memset */ #include /* for select timeout */ #include /* for select */ #include /* for inet_* routines */ #include /* for signals */ /*** *** int dl_el_startele(char *service) *** *** Function: start an election for all clients on the port specified *** by service *** Return : DL_OK if success *** DL_ERROR if error *** Restrictions: note that a client must also be running *** for this process to participate in the election ***/ int dl_el_startele(char *service) { int bsock; /* send socket */ char buffer[DL_MAXLINE]; /* send buffer */ /* text to send. elections always start at 0 */ strcpy(buffer,"E 0 0\r\n"); /* open broadcast socket */ bsock=dl_sck_sockb(); if (bsock==DL_ERROR) { #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: error opening socket\n"); #endif return DL_ERROR; } if (dl_sck_sendb(bsock,service,buffer) == DL_ERROR) { /* error ? how could this happen ? */ #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: error sending text\n"); #endif return DL_ERROR; } /* close socket */ dl_sck_close(bsock); return DL_OK; } /*** *** thread_t dl_el_startserver(char *service, \ *** void(*function)(char *winner,int winport, int myport)) *** *** Function: start a server for the election port specified by service *** that is participating in elections from now on *** after an election function is called with the winner as *** argument *** Return : the thread id of the server *** DL_ERROR if error ***/ static struct arg_struct { /* needed for passing all the data to thread */ char service[20]; void (*function)(char *winner,int winport, int myport); } arg; thread_t dl_el_startserver(char *service, \ void(*function)(char *winner,int winport, int myport)) { thread_t mythread; /* thread id of newly created thread */ void *dl_el_server(void *arg); /* function to start thread with */ /* pack arguments into structure */ strcpy(arg.service,service); arg.function=function; /* start thread */ mythread = dl_thr_create(dl_el_server,(void *)&arg); /* and exit */ return mythread; } /*** *** int dl_el_stopserver(thread_t server) *** *** Function: stop the specified server from participating *** in elections *** Return : DL_OK if success *** DL_ERROR if error ***/ int dl_el_stopserver(thread_t server) { return(dl_thr_kill(server,DL_EL_SIGNAL)); } /*** *** void dl_el_exitserver(int signal) *** *** Function: stop the election server *** Return : - ***/ static int myport; /* port for socket ; needed global for */ /* use in signal handler, sorry ;-) */ static int intport; /* the port of the distributor ; also global */ void dl_el_exitserver(int signal) { struct sockaddr_in localhost; /* an IEA */ char buffer[DL_MAXLINE]; /* send buffer */ int sock; /* send socket */ /* unsubscribe with distributor */ localhost.sin_addr.s_addr=INADDR_LOOPBACK; localhost.sin_family=AF_INET; localhost.sin_port=intport; /* create communication socket */ sock=socket(PF_INET,SOCK_DGRAM,IPPROTO_UDP); /* message to send */ sprintf(buffer,"R %d\r\n",myport); /* here it goes */ sendto(sock,buffer,strlen(buffer)+1,0, \ (struct sockaddr *)&localhost,sizeof(localhost)); /* and exit */ dl_thr_exit(); } /*** *** void *dl_el_server(void *arg) *** *** Function: the election server. wait for and parse requests *** Return : values != NULL indicate an error *** detailed return errors to be specified when needed ***/ void *dl_el_server(void *arg) { char service[20]; /* the port for internal use ; as string */ void(*function)(); /* the function to call when election is over */ int distsendsock; /* socket used for sending to distributor */ int distrecsock; /* socket used for receiving from distributor */ int bsock; /* socket used for broadcasting */ int s; /* socket used for various purposes */ struct sockaddr_in dist_sin; /* an IEA */ struct sockaddr_in todist; /* an IEA */ struct sockaddr_in *sin_ptr; /* an IEA ptr */ fd_set sockfds; /* file descriptor set for select */ int maxsockfds=0; /* maximum descriptor used in sockfds */ struct timeval timeout; /* timeout with select */ int has_data; /* number of descriptors from select */ int election; /* flag election is running */ int winflag; /* flag can we still become the winner */ struct arg_struct *argptr; /* I hate conversions ;-) */ unsigned int ipsum,myipsum; /* IP numbers used in election */ unsigned int ipport; /* IP ports used in election */ char buffer[DL_MAXLINE]; /* I/O buffer string */ int reclen; /* return length from recv */ char winner[20]; /* winner of election */ int winport; /* winner of election */ /* get all the arguments back */ argptr=(struct arg_struct *)arg; strcpy(service,argptr->service); intport=dl_sck_getport(argptr->service,DL_SCK_UDP); function=argptr->function; /* check if distributor is allready running */ s=dl_sck_server(service,DL_SCK_UDP,NULL); if (s != DL_ERROR) { dl_sck_close(s); /* start distributor */ /* we use fork here, because the distributor shouldn't be */ /* tied to any specific process */ switch(fork()) { /*** child ***/ case 0: #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: launching distributor\n"); #endif execl("distrib","distrib",service,NULL); /* you'll never return from here */ exit(0); /*** parent ***/ default: /* wait a bit so the distributor has time to start */ sleep(2); } } else { #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: distributor allready running\n"); #endif } /* create broadcast socket */ bsock=dl_sck_sockb(); if (bsock == 0) { #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: can't open broadcast socket\n"); #endif dl_thr_exit(); } /* now create the distributor sockets */ /* need to do this by hand because sin is needed */ distsendsock=socket(PF_INET,SOCK_DGRAM,IPPROTO_UDP); if (distsendsock == -1) { #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: can't create distsendsock\n"); #endif dl_thr_exit(); } /* where to send from todist */ todist.sin_addr.s_addr = INADDR_LOOPBACK; todist.sin_family = AF_INET; todist.sin_port = intport; distrecsock=socket(PF_INET,SOCK_DGRAM,IPPROTO_UDP); if (distrecsock == -1) { #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: can't create distrecsoc\n"); #endif dl_thr_exit(); } /* now scan for a free port and bind */ dist_sin.sin_family = AF_INET; dist_sin.sin_addr.s_addr = INADDR_LOOPBACK; myport = DL_EL_PORTB; dist_sin.sin_port = htons(myport); while (bind(distrecsock,(struct sockaddr *)&dist_sin, \ sizeof(dist_sin)) == -1 && /* bind sucessfull ? */ myport < DL_EL_PORTB + 1000 && /* we only scan 1000 ports */ myport < 65534 ) { /* and only up to maximum */ myport++; dist_sin.sin_port = htons(myport); } /* error ? */ if (myport >= DL_EL_PORTB + 1000 || myport >= 65534) { #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: can't bind socket\n"); #endif dl_thr_exit(); } /* and yet another socket for calculationg the election data */ s=socket(PF_INET,SOCK_DGRAM,IPPROTO_UDP); /* calculate my own data */ sin_ptr=dl_sck_getifadr(); myipsum = sin_ptr->sin_addr.s_addr; close(s); #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: myipsum = %x - myport = %d \n",myipsum,myport); #endif /* now register with distributor */ sprintf(buffer,"A %d\r\n",myport); sendto(distsendsock,buffer,strlen(buffer)+1,0, \ (struct sockaddr *)&todist,sizeof(todist)); /* routine for exiting server */ dl_sig_catch(DL_EL_SIGNAL,dl_el_exitserver); /* prepare everything for select */ timeout.tv_sec = (DL_EL_TIMEOUT) / 1000; timeout.tv_usec = (DL_EL_TIMEOUT) % 1000; maxsockfds=((distrecsock+1) > maxsockfds ? (distrecsock+1) : maxsockfds); /* init values */ election=0; winflag=1; /* wait for elections */ while(1) { /* prepare for next select */ FD_ZERO(&sockfds); FD_SET(distrecsock,&sockfds); /* check if received data pending */ #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: vor select\n"); #endif has_data = select(maxsockfds,&sockfds, \ (fd_set *)NULL,(fd_set *)NULL,&timeout); #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: select returned %d\n",has_data); #endif /* check result of select */ switch (has_data) { /*** timeout ***/ case 0: #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: select timeout\n"); #endif /* are we doing an election ? */ if (election) { /* timeout in election */ /* -> no one is answering any more */ /* -> we could be the winner */ /* election is over */ election=0; /* if we could be winner, then we really are winner */ if (winflag) { sprintf(buffer,"W %s %u\r\n",inet_ntoa(sin_ptr->sin_addr),myport); dl_sck_sendb(bsock,service,buffer); } } /* now continue with next read */ break; /* from switch (has_data) */ /*** there's a message waiting for us ***/ case 1: /* get message */ reclen=recv(distrecsock,buffer,sizeof(buffer),0); if (reclen<=0) { #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: recv error"); #endif break; /* from switch (has_data) */ } #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: received #%s#\n",buffer); #endif /* what kind of message */ switch(buffer[0]) { /* Election 'E ipsum port' */ case 'E': /* parse message */ if (sscanf(buffer,"E %d %d\r\n",&ipsum,&ipport) != 2) { #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: wrong message format\n"); #endif break; /* from switch (buffer[0]) */ } /* if we can't win anymore, stop here */ if (winflag==0 && ipsum!=0 && ipport!=0) { #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: discarding message #%s#\n",buffer); #endif break; /* from switch (buffer[0]) */ } /* now we are doing an election */ election=1; /* modified bully election algorithm */ /* should I participate in election anymore ? */ if ((myipsum > ipsum) || \ (myipsum == ipsum && myport > ipport)) { #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: continuing with election\n"); fprintf(stderr,"LIBDIST-ele: myipsum = %u\n",myipsum); fprintf(stderr,"LIBDIST-ele: ipsum = %u\n",ipsum); fprintf(stderr,"LIBDIST-ele: myport = %u\n",myport); fprintf(stderr,"LIBDIST-ele: ipport = %u\n",ipport); #endif /* send new election string */ /* ATTENTION: as the UDP packets could */ /* get lost without notification, our */ /* election would totally mess up, if */ /* this happens. So you better use it */ /* only with reliable networks */ sprintf(buffer,"E %u %u\r\n",myipsum,myport); dl_sck_sendb(bsock,service,buffer); } else if (myipsum==ipsum && myport==ipport) { /* sometimes we get phantom messages */ /* really dont know where they */ /* come from, this is only a */ /* work-around */ break; } else { /* as we don't participate any more */ /* we will never be the winner of this */ #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: retreating from election\n"); #endif winflag=0; } break; /* from switch (buffer[0]) */ /*** Winner 'W ip-addr port' ***/ case 'W': /* parse message */ if (sscanf(buffer,"W %s %d\r\n",winner,&winport) != 2) { #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: wrong message format\n"); #endif break; /* from switch (buffer[0]) */ } /* call function with argument winner */ function(winner,winport,myport); /* election time is over, reset flags */ election=0; winflag=1; break; /* from switch (buffer[0]) */ /*** Default -> Protocol error ***/ default: #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: protocol error\n"); #endif } /* switch (buffer[0]) */ break; /* from switch (has_data) */ /*** Default -> select error ***/ default: #ifdef DEBUG fprintf(stderr,"LIBDIST-ele: select error\n"); #endif } /* switch (has_data) */ } /* while */ }