/* Fork Join Example Demonstrates how to spawn processes and exchange messages */ /* defines and prototypes for the PVM library */ #include <pvm3.h> /* Maximum number of children this program will spawn */ #define MAXNCHILD 20 /* Tag to use for the joing message */ #define JOINTAG 11
int main(int argc, char* argv[]) { /* number of tasks to spawn, use 3 as the default */ int ntask = 3; /* return code from pvm calls */ int info; /* my task id */ int mytid; /* my parents task id */ int myparent; /* children task id array */ int child[MAXNCHILD]; int i, mydata, buf, len, tag, tid;
/* find out my task id number */ mytid = pvm_mytid(); /* check for error */ if (mytid < 0) { /* print out the error */ pvm_perror(argv[0]); /* exit the program */ return -1; } /* find my parent's task id number */ myparent = pvm_parent(); /* exit if there is some error other than PvmNoParent */ if ((myparent < 0) && (myparent != PvmNoParent)) { pvm_perror(argv[0]); pvm_exit(); return -1; }
/* if i don't have a parent then i am the parent */ if (myparent == PvmNoParent) { /* find out how many tasks to spawn */ if (argc == 2) ntask = atoi(argv[1]); /* make sure ntask is legal */ if ((ntask < 1) || (ntask > MAXNCHILD)) { pvm_exit(); return 0; } /* spawn the child tasks */ info = pvm_spawn(argv[0], (char**)0, PvmTaskDefault, (char*)0, ntask, child); /* print out the task ids */ for (i = 0; i < ntask; i++) if (child[i] < 0) /* print the error code in decimal*/ printf(" %d", child[i]); else /* print the task id in hex */ printf("t%x\t", child[i]); putchar('\n');
/* make sure spawn succeeded */ if (info == 0) { pvm_exit(); return -1; } /* only expect responses from those spawned correctly */ ntask = info; for (i = 0; i < ntask; i++) { /* recv a message from any child process */ buf = pvm_recv(-1, JOINTAG); if (buf < 0) pvm_perror("calling recv"); info = pvm_bufinfo(buf, &len, &tag, &tid); if (info < 0) pvm_perror("calling pvm_bufinfo"); info = pvm_upkint(&mydata, 1, 1); if (info < 0) pvm_perror("calling pvm_upkint"); if (mydata != tid) printf("This should not happen!\n"); printf("Length %d, Tag %d, Tid t%x\n", len, tag, tid); } pvm_exit(); return 0; }
/* i'm a child */ info = pvm_initsend(PvmDataDefault); if (info < 0) { pvm_perror("calling pvm_initsend"); pvm_exit(); return -1; } info = pvm_pkint(&mytid, 1, 1); if (info < 0) { pvm_perror("calling pvm_pkint"); pvm_exit(); return -1; } info = pvm_send(myparent, JOINTAG); if (info < 0) { pvm_perror("calling pvm_send"); pvm_exit(); return -1; } pvm_exit(); return 0; }
Figure shows the output of running forkjoin. Notice that the order the messages were received is nondeterministic. Since the main loop of the parent processes messages on a first-come first-serve basis, the order of the prints are simply determined by time it takes messages to travel from the child tasks to the parent .
% forkjoin t10001c t40149 tc0037 Length 4, Tag 11, Tid t40149 Length 4, Tag 11, Tid tc0037 Length 4, Tag 11, Tid t10001c % forkjoin 4 t10001e t10001d t4014b tc0038 Length 4, Tag 11, Tid t4014b Length 4, Tag 11, Tid tc0038 Length 4, Tag 11, Tid t10001d Length 4, Tag 11, Tid t10001e