Added initial inter-process communication: Sharing pids between processes.

[wsti_so.git] / src / process3.c

diff --git a/src/process3.c b/src/process3.c
index 8b4f8264f39a3621f6dc0f267b6f53e8339e0f63..b1b997212be53430306b69232a3c88bd7d2f3b14 100644 (file)
--- a/src/process3.c
+++ b/src/process3.c
@@ -1,27 +1,71 @@
 #include <stdio.h>
 
+/* exit.. */
+#include <stdlib.h>
+
 /* open/read/write/close */
 #include <fcntl.h>
 
 /* Signals handling.. */
 #include <signal.h>
 
+#include <sys/shm.h>
+
+/** Named pipe used to communicate with process2 */
+char * read_pipe = "/tmp/process2pipe";
+
+/** Descriptor of input pipe */
+int read_descriptor;
+
+
+/**
+ * Shared memory variables
+ */
+/**
+ * Memory key for processes. Must be same between all processes to properly
+ * communicate.
+ */
+key_t shmkey = 18912;
+/**
+ * Id of the shared memory
+ */
+int shmid;
+
+/**
+ * Message shared by processes. Contains array of process IDs
+ */
+struct message {
+       pid_t pids[3];
+};
+
+struct message * processes = NULL;
+
+
 /**
  * Handler for signals.
  */
 void sig_handler(int signo)
 {
+       fprintf(stderr, "[%s] Received %s!\n", "process3", strsignal(signo));
        if (signo == SIGUSR1) {
-               fprintf(stderr, "[%s] SIGUSR1!\n", "process1");
        }
-       else if (signo == SIGUSR2) {
-               fprintf(stderr, "[%s] SIGUSR2!\n", "process1");
+       else if (signo == SIGTERM) {
+               int i = 0;
+               fprintf(stderr, "[%s] > Releasing resources\n", "process3");
+               close(read_descriptor);
+               for (; i < 3; i++) {
+                       fprintf(stderr, "[%s] Process %d, PID: %d\n", "process3", i, processes->pids[i]);
+               }
+               exit(0);
        }
-       else if (signo == SIGINT) {
-               fprintf(stderr, "[%s] SIGINT!\n", "process1");
+       else if (signo == SIGTSTP) {
+               fprintf(stderr, "[%s] > Closing pipe\n", "process3");
+               close(read_descriptor);
+               raise (SIGSTOP);
        }
        else if (signo == SIGCONT) {
-               fprintf(stderr, "[%s] SIGCONT!\n", "process1");
+               fprintf(stderr, "[%s] > Opening pipe\n", "process3");
+               read_descriptor = open(read_pipe, O_RDONLY);
        }
 }
 
@@ -30,12 +74,6 @@ void sig_handler(int signo)
  * grabbed data to the standard output.
  */
 int main(void) {
-       /** Named pipe used to communicate with process2 */
-       char * read_pipe = "/tmp/process2pipe";
-
-       /** Descriptor of input pipe */
-       int read_descriptor;
-
        /** Buffer used for storing data from input pipe */
        int buffer = 0;
        
@@ -50,16 +88,25 @@ int main(void) {
        if (signal(SIGUSR1, sig_handler) == SIG_ERR) {
                fprintf(stderr, "can't catch SIGUSR1\n");
        }
-       if (signal(SIGUSR2, sig_handler) == SIG_ERR) {
-               fprintf(stderr, "can't catch SIGUSR2\n");
+       if (signal(SIGTERM, sig_handler) == SIG_ERR) {
+               fprintf(stderr, "can't catch SIGTERM\n");
        }
-       if (signal(SIGINT, sig_handler) == SIG_ERR) {
-               fprintf(stderr, "can't catch SIGINT\n");
+       if (signal(SIGTSTP, sig_handler) == SIG_ERR) {
+               fprintf(stderr, "can't catch SIGTSTP\n");
        }
        if (signal(SIGCONT, sig_handler) == SIG_ERR) {
                fprintf(stderr, "can't catch SIGCONT\n");
        }
 
+       /*
+        * Register memory to share with other processes, and pass current
+        * process id to the array.
+        */
+       shmid = shmget(shmkey, sizeof(struct message), IPC_CREAT | 0666);
+
+       processes = (struct message *)shmat(shmid, NULL, 0);
+       processes->pids[2] = getpid();
+
        /* Reading from process2 */
        read_descriptor = open(read_pipe, O_RDONLY);
 
@@ -77,6 +124,7 @@ int main(void) {
                }
        }
 
+       /* Release resources in normal program flow exit. */
        close(read_descriptor);
 
        return 0;