# HG changeset patch
# User Markus Bröker <mbroeker@largo.dyndns.tv>
# Date 1254041809 -7200
# Node ID 244356bc3a2015afdadeb9cae7db4e1fae3142a5
# Parent  a540a842ddef5b975ae94514a6dbcd405ba9aaa5
Pipes and COPY-ON-WRITE

In this example, every forked process gets its own copy of the
countervariable i through copy-on-write.

committer: Markus Bröker <mbroeker@largo.homelinux.org>

diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
      CC = gcc -g -ggdb $(PROF)
     CPP = g++ -g -ggdb $(PROF)
- CFLAGS = -Wall -O2 -Iinclude -ansi
+ CFLAGS = -Wall -O2 -Iinclude #-ansi
      RM = rm -f
    FIND = find
 
@@ -67,6 +67,7 @@
 TARGET += numbers
 TARGET += nearest
 TARGET += cppdatabase
+TARGET += pipe
 
 .SUFFIXES: .c .cc .asm
 
@@ -322,6 +323,11 @@
 	@echo Linking $<...
 	@$(CPP) -Wall -O2 -g -ggdb $< -o $@
 
+pipe: pipe.o
+	@echo Linking $<...
+	@$(CC) -Wall -O2 -g -ggdb $< -o $@
+
+
 .PHONY: beauty clean uninstall
 
 clean:
diff --git a/pipe.c b/pipe.c
new file mode 100644
--- /dev/null
+++ b/pipe.c
@@ -0,0 +1,69 @@
+/**
+ * pipe.c
+ * Copyright (C) 2009 Markus Broeker
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <wait.h>
+#include <assert.h>
+
+#define MAX 50
+
+int main (int argc, char **argv)
+{
+    int tube[2];
+    int i, status, count = 0;
+
+    pid_t pid;
+
+    char buffer[80];
+
+    for (i = 0; i < MAX; i++) {
+        if (pipe (tube) == -1) {
+            perror ("PIPE");
+
+            return EXIT_FAILURE;
+        }
+
+        pid = fork ();
+        switch (pid) {
+        case 0:
+            // we only want to write
+            close (tube[0]);
+
+            /**
+             * copy on write: every forked process gets its own copy of i
+             *                and the magic of synchronization works
+             */
+            for (i = 0; i < MAX; i++)
+                status = write (tube[1], "MESSAGE FROM SON\n", 17);
+            break;
+
+        case -1:
+            printf ("ERROR");
+            break;
+
+        default:
+            printf ("Son started as pid %d\n", pid);
+
+            // we only want to read...
+            close (tube[1]);
+
+            FILE *f = fdopen (tube[0], "r");
+            assert (f != NULL);
+            while (fgets (buffer, sizeof (buffer), f) != NULL) {
+                printf ("FATHER RECEIVED [%4d]: %s", count++, buffer);
+            }
+
+            if (fclose (f) < 0)
+                perror ("fclose");
+
+            printf ("PID [%4d] has finished...\n", wait (&pid));
+        }
+    }
+
+    return EXIT_SUCCESS;
+}