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 f06a381014d060f61d11baafe896d8d911b75282..b1b997212be53430306b69232a3c88bd7d2f3b14 100644 (file)
--- a/src/process3.c
+++ b/src/process3.c
@@ -1,33 +1,115 @@
 #include <stdio.h>
+
+/* exit.. */
 #include <stdlib.h>
-#include <string.h>
 
 /* open/read/write/close */
 #include <fcntl.h>
 
-/** If buffer is too small to hold entire string, it is incremented by this value */
-#define BUFFER_STEP 16
+/* 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) {
+       }
+       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 == SIGTSTP) {
+               fprintf(stderr, "[%s] > Closing pipe\n", "process3");
+               close(read_descriptor);
+               raise (SIGSTOP);
+       }
+       else if (signo == SIGCONT) {
+               fprintf(stderr, "[%s] > Opening pipe\n", "process3");
+               read_descriptor = open(read_pipe, O_RDONLY);
+       }
+}
 
 /**
  * Program grabs data (calculated number of characters) from process2 and prints
  * grabbed data to the standard output.
  */
 int main(void) {
-       /** Named pipe used to communicate with process2 */
-       char * read_pipe = "/tmp/process2pipe";
-
-       int read_descriptor;
-       
+       /** Buffer used for storing data from input pipe */
        int buffer = 0;
        
-       int i = 0;
+       /** Stores number of bytes read from input pipe in current iteration */
        ssize_t count = 0;
 
+       fprintf(stderr, "[%s] Init!\n", "process3");
+
+       /**
+        * Register signals handled by process
+        */
+       if (signal(SIGUSR1, sig_handler) == SIG_ERR) {
+               fprintf(stderr, "can't catch SIGUSR1\n");
+       }
+       if (signal(SIGTERM, sig_handler) == SIG_ERR) {
+               fprintf(stderr, "can't catch SIGTERM\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);
 
-       int number_of_characters = 0;
-       
        while(1) {
                /* Read data from input pipe */
                count = read(read_descriptor, &buffer, sizeof(int));
@@ -42,6 +124,7 @@ int main(void) {
                }
        }
 
+       /* Release resources in normal program flow exit. */
        close(read_descriptor);
 
        return 0;