experiments

commit 59f3c21dab258363031fcd995d6801eb0ea75666
parent af093765d73c4ad9f0c82f593316c6de8f5b5525
Author: Vetle Haflan <vetle@haflan.dev>
Date:   Sun,  8 Mar 2020 19:41:25 +0100

Add poll() example (with fifo)

Diffstat:
A
c/linux_system/02-io/fifo_poll.c
 | 
63
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
A
c/linux_system/fifo_thread.c
 | 
55
+++++++++++++++++++++++++++++++++++++++++++++++++++++++

2 files changed, 118 insertions(+), 0 deletions(-)
diff --git a/c/linux_system/02-io/fifo_poll.c b/c/linux_system/02-io/fifo_poll.c
@@ -0,0 +1,63 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <stdbool.h>
+#include <unistd.h>
+
+#define MAX_BUF 1024
+
+// Example use of poll()
+// Reads from and writes to same fifo, using poll() to watch POLLIN and POLLOUT
+// events and act when the fd is ready
+
+char * myfifo = "./this.fifo";
+
+int main()
+{
+	int fd;
+	/* create the FIFO (named pipe) */
+	mkfifo(myfifo, 0666);
+	/* open in nonblock to avoid waiting */
+	fd = open(myfifo, O_RDWR);
+	if (fd == -1) {
+		printf("main: %d\n", errno);
+		return 1;
+	}
+
+	// Variables to write return values and read data to 
+	int len, ret;
+	char input[MAX_BUF], output[MAX_BUF];
+
+	// Define array of pfd(s). Only one file descriptor in this case
+	struct pollfd pfds[1]; 
+	pfds[0].fd = fd;
+	pfds[0].events = POLLIN | POLLOUT; // Watch poll in and out events
+	while (strcmp(input, "exit\n")) {
+		ret = poll(pfds, 1, 1); 	// 1 fd, 1 second timeout
+		if (ret == -1) {
+			perror("poll");
+			return 1;
+		}
+		if (!ret) {
+			continue;
+		}
+		if (pfds[0].revents & POLLIN) {
+			len = read(fd, output, MAX_BUF);
+			printf("Received: %d bytes\n", len);
+			output[len] = '\0'; // ignore garbage from previous read
+			printf("Received: %s", output);
+			continue;
+		}
+		if (pfds[0].revents & POLLOUT) {
+			printf("> ");
+			fgets(input, MAX_BUF, stdin);
+			write(fd, input, strlen(input));
+		}
+	}
+	close(fd);
+
+	return 0;
+}
diff --git a/c/linux_system/fifo_thread.c b/c/linux_system/fifo_thread.c
@@ -0,0 +1,55 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <pthread.h>
+
+#define MAX_BUF 1024
+
+char * myfifo = "./this.fifo";
+
+void * read_fifo() {
+	// open, read, and display the message from the FIFO
+	int fd = open(myfifo, O_RDONLY);
+	if (fd == -1) {
+		printf("read_fifo: %d", errno);
+	}
+	char buf[MAX_BUF];
+	while (strcmp(buf, "exit")) {
+		int len = read(fd, buf, MAX_BUF);
+		printf("Received: %d bytes\n", len);
+		printf("Received: %s\n", buf);
+		if (!strcmp(buf, "exit")) {
+			printf("Should exit");
+		}
+	}
+	close(fd);
+}
+
+int main()
+{
+	int fd;
+	/* create the FIFO (named pipe) */
+	mkfifo(myfifo, 0666);
+	/* open in nonblock to avoid waiting */
+	pthread_t read_thread;
+	pthread_create(&read_thread, NULL, read_fifo, (void *) NULL);
+	fd = open(myfifo, O_WRONLY | O_ASYNC);
+	if (fd == -1) {
+		printf("main: %d\n", errno);
+		return 1;
+	}
+	/* write to the FIFO */
+	char input[MAX_BUF];
+	while (strcmp(input, "exit")) {
+		fgets(input, MAX_BUF, stdin);
+		write(fd, input, strlen(input));
+	}
+	pthread_join(read_thread, NULL);
+	close(fd);
+
+	return 0;
+}