/phlog/mmap.gph on kroovy.de

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	A minimal example of C's syscall mmap() to share memory between processes
	=========================================================================

	Recently I decided to add a feature to bsleep:
	My idea was to show the last button pressed (other than 'b', which would
	interrupt the sleep).

	The problem to overcome was the following:
	When fork() is used, parent and child no longer can access each others
	variables.
	Since it's the parent-process reading the button pressed, while the child
	is printing the update. Therefore the child needs to read the character
	from the parent process.
	Using mmap() I added a pointer to 1 byte of memory which both processes
	can access. It stores the character of the last button pressed.

	As a result bsleep has become a minimal example of:
	- how to fork a process in C
	- how to exchange data between parent and child process using mmap()

	git clone git://kroovy.de/bsleep

	Build dependencies
	- C compiler
	- libc


	#define _POSIX_SOURCE
	#include <signal.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <sys/mman.h>
	#include <unistd.h>

	int
	main(void)
	{
	int i;
	char *shmem = mmap(NULL, sizeof(char), PROT_READ \| PROT_WRITE, MAP_SH…
	pid_t pid = fork();

	if (pid == 0) {
	/* CHILD */
	for (i=1;;i++) {
	printf("\r[ press 'b' to interrupt: %ds ] [ '%c' was pressed …
	fflush(stdout);
	sleep(1);
	}
	} else {
	/* PARENT */
	system("/bin/stty raw -echo");
	while ((*shmem = getchar()) != 'b');
	kill(pid, SIGKILL);
	system("/bin/stty cooked echo");
	printf("\n");
	}
	}


	In the near future I will consider adding error-handling and will have a
	look at pagesize. It might be a good idea to let mmap claim a page-aligned
	amount of bytes. Not sure at this point.