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

[wsti_so.git] / src / process2.c

diff --git a/src/process2.c b/src/process2.c
index 7ae70ffc4a056bfd4dfaaa21278c3537f89438ba..2417fe88638fd27bdc543a5d764bca6847540b87 100644 (file)
--- a/src/process2.c
+++ b/src/process2.c
@@ -1,4 +1,6 @@
 #include <stdio.h>
+/* exit.. */
+#include <stdlib.h>
 
 /* open/read/write/close */
 #include <fcntl.h>
@@ -6,25 +8,77 @@
 /* Signals handling.. */
 #include <signal.h>
 
+#include <sys/shm.h>
+
 /** If buffer is too small to hold entire string, it is incremented by this value */
 #define BUFFER_STEP 16
 
+/** Named pipe used to communicate with process1 */
+char * read_pipe = "/tmp/process1pipe";
+
+/** Named pipe used to communicate with process3 */
+char * write_pipe = "/tmp/process2pipe";
+
+/** Descriptor of input pipe */
+int read_descriptor;
+
+/** Descriptor of output pipe */
+int write_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", "process2", 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", "process2");
+               close(read_descriptor);
+               close(write_descriptor);
+               unlink(write_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 pipes\n", "process2");
+               close(read_descriptor);
+               close(write_descriptor);
+               raise (SIGSTOP);
        }
        else if (signo == SIGCONT) {
-               fprintf(stderr, "[%s] SIGCONT!\n", "process1");
+               fprintf(stderr, "[%s] > Opening pipes\n", "process2");
+               read_descriptor = open(read_pipe, O_RDONLY);
+               write_descriptor = open(write_pipe, O_WRONLY);
        }
 }
 
@@ -33,18 +87,6 @@ void sig_handler(int signo)
  * and pass the value to process3.
  */
 int main(void) {
-       /** Named pipe used to communicate with process1 */
-       char * read_pipe = "/tmp/process1pipe";
-
-       /** Named pipe used to communicate with process3 */
-       char * write_pipe = "/tmp/process2pipe";
-
-       /** Descriptor of input pipe */
-       int read_descriptor;
-
-       /** Descriptor of output pipe */
-       int write_descriptor;
-
        /**
         * Buffer used for storing data from input pipe.
         * Data is stored in chunks of BUFFER_STEP size.
@@ -59,13 +101,6 @@ int main(void) {
        /** Stores number of bytes read from input pipe in current iteration */
        ssize_t count = 0;
 
-       /* Reading from process1 */
-       read_descriptor = open(read_pipe, O_RDONLY);
-
-       /* Writing to process2 */
-       mkfifo(write_pipe, 0666);
-       write_descriptor = open(write_pipe, O_WRONLY);
-
        int number_of_characters = 0;
 
        fprintf(stderr, "[%s] Init!\n", "process2");
@@ -76,16 +111,32 @@ 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[1] = getpid();
+
+       /* Reading from process1 */
+       read_descriptor = open(read_pipe, O_RDONLY);
+
+       /* Writing to process2 */
+       mkfifo(write_pipe, 0666);
+       write_descriptor = open(write_pipe, O_WRONLY);
+
        while(1) {
                /* Read data from input pipe */
                count = read(read_descriptor, buffer, BUFFER_STEP);
@@ -107,6 +158,7 @@ int main(void) {
                }
        }
 
+       /* Release resources in normal program flow exit. */
        close(read_descriptor);
        close(write_descriptor);
        unlink(write_descriptor);