linked list elements gone?
- by Hristo
I create a linked list dynamically and initialize the first node in main(), and I add to the list every time I spawn a worker process. Before the worker process exits, I print the list. Also, I print the list inside my sigchld signal handler.
in main():
head = NULL;
tail = NULL;
// linked list to keep track of worker process
dll_node_t *node;
node = (dll_node_t *) malloc(sizeof(dll_node_t)); // initialize list, allocate memory
append_node(node);
node->pid = mainPID; // the first node is the MAIN process
node->type = MAIN;
in a fork()'d process:
// add to list
dll_node_t *node;
node = (dll_node_t *) malloc(sizeof(dll_node_t));
append_node(node);
node->pid = mmapFileWorkerStats->childPID;
node->workerFileName = mmapFileWorkerStats->workerFileName;
node->type = WORK;
functions:
void append_node(dll_node_t *nodeToAppend) {
/*
* append param node to end of list
*/
// if the list is empty
if (head == NULL) {
// create the first/head node
head = nodeToAppend;
nodeToAppend->prev = NULL;
} else {
tail->next = nodeToAppend;
nodeToAppend->prev = tail;
}
// fix the tail to point to the new node
tail = nodeToAppend;
nodeToAppend->next = NULL;
}
finally... the signal handler:
void chld_signalHandler() {
dll_node_t *temp1 = head;
while (temp1 != NULL) {
printf("2. node's pid: %d\n", temp1->pid);
temp1 = temp1->next;
}
int termChildPID = waitpid(-1, NULL, WNOHANG);
dll_node_t *temp = head;
while (temp != NULL) {
if (temp->pid == termChildPID) {
printf("found process: %d\n", temp->pid);
}
temp = temp->next;
}
return;
}
Is it true that upon the worker process exiting, the SIGCHLD signal handler is triggered? If so, that would mean that after I print the tree before exiting, the next thing I do is in the signal handler which is print the tree... which would mean i would print the tree twice?
But the tree isn't the same. The node I add in the worker process doesn't exist when I print in the signal handler or at the very end of main(). Any idea why?
Thanks,
Hristo
