From e4dce6b0d0a465f792d1de70c0c65c2fcb8d196c Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@sbcglobal.net>
Date: Sat, 12 Mar 2016 02:51:12 -0500
Subject: fixity fix

---
 mpjpeg.c | 42 +++++++++++++++++++++++++++---------------
 1 file changed, 27 insertions(+), 15 deletions(-)

(limited to 'mpjpeg.c')

diff --git a/mpjpeg.c b/mpjpeg.c
index b64c5f0..87ca2a4 100644
--- a/mpjpeg.c
+++ b/mpjpeg.c
@@ -1,10 +1,11 @@
 /* Copyright 2016 Luke Shumaker */
 
+#include <errno.h>
+#include <error.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
-#include <error.h>
 
 #include "mpjpeg.h"
 #include "util.h"
@@ -47,14 +48,16 @@ void mpjpeg_reader(struct mpjpeg_stream *s, int fd, const char *boundary) {
 
 	while (1) {
 		s->back->len = -1;
-		/* read the frame header (MIME headers) */
+		/* scan for the first non-empty line */
 		do {
 			line_len = getline(&line_buf, &line_cap, stream);
 		} while (line_len >= 0 && strcmp(line_buf, "\r\n") == 0);
+		/* make sure it matches the boundary separator */
 		if (strcmp(line_buf, boundary) != 0) {
 			error(0, 0, "line does not match boundary: \"%s\"", line_buf);
 			return;
 		}
+		/* read the frame header (MIME headers) */
 		while (strcmp(line_buf, "\r\n") != 0 && line_len >= 0) {
 			line_len = getline(&line_buf, &line_cap, stream);
 			if (strncasecmp(line_buf, "Content-length:", strlen("Content-length:")) == 0) {
@@ -75,35 +78,44 @@ void mpjpeg_reader(struct mpjpeg_stream *s, int fd, const char *boundary) {
 		}
 
 		/* swap the frames */
-		pthread_mutex_lock(&s->frontlock);
+		pthread_rwlock_wrlock(&s->frontlock);
 		struct frame *tmp = s->front;
 		s->front = s->back;
 		s->back = tmp;
-		pthread_mutex_unlock(&s->frontlock);
+		s->framecount++;
+		pthread_rwlock_unlock(&s->frontlock);
 	}
 
 }
 
 void mpjpeg_writer(struct mpjpeg_stream *s, int fd, const char *boundary) {
 	struct frame myframe = { 0 };
-	struct frame *lastframe = NULL;
+	long lastframe = 0;
+	pthread_rwlock_rdlock(&s->frontlock);
 	while(1) {
 		/* get the most recent frame (copy front to myframe) */
-		pthread_mutex_lock(&s->frontlock);
-		if (s->front == lastframe) { /* TODO: use a pthread_cond_t instead of a busy loop */
-			pthread_mutex_unlock(&s->frontlock);
-			continue;
-		}
 		if (myframe.cap < (size_t)s->front->len)
 			myframe.data = xrealloc(myframe.data, myframe.cap = s->front->len);
 		memcpy(myframe.data, s->front->data, myframe.len = s->front->len);
-		lastframe = s->front;
-		pthread_mutex_unlock(&s->frontlock);
+		lastframe = s->framecount;
+		pthread_rwlock_unlock(&s->frontlock);
 		/* send the frame to the client */
-		if (dprintf(fd, "--%s\r\nContent-Type: image/jpeg\r\nContent-Length: %zd\r\n\r\n", boundary, myframe.len) < 0)
+		if (dprintf(fd, "--%s\r\nContent-Type: image/jpeg\r\nContent-Length: %zd\r\n\r\n", boundary, myframe.len) < 0) {
+			error(0, errno, "dprintf");
 			return;
-		if (write(fd, myframe.data, myframe.len) < myframe.len)
+		}
+		if (write(fd, myframe.data, myframe.len) < myframe.len) {
+			error(0, errno, "write");
 			return;
+		}
+
+		/* poll until there's a new frame */
+		pthread_rwlock_rdlock(&s->frontlock);
+		while (s->framecount == lastframe) {
+			pthread_rwlock_unlock(&s->frontlock);
+			usleep(30000); /* a bit over 30 FPS */
+			pthread_rwlock_rdlock(&s->frontlock);
+		}
 	}
 }
 
@@ -112,5 +124,5 @@ void init_mpjpeg_stream(struct mpjpeg_stream *s) {
 	ZERO(s->b);
 	s->front = &s->a;
 	s->back = &s->b;
-	pthread_mutex_init(&s->frontlock, NULL);
+	pthread_rwlock_init(&s->frontlock, NULL);
 }
-- 
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