From d24297abf4390e88a972e67ba3fb35fe688d831f Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@sbcglobal.net>
Date: Tue, 12 Apr 2016 01:07:39 -0400
Subject: multipart-replace: use condition variables instead of polling

---
 src/multipart-replace.c | 22 ++++++++--------------
 src/multipart-replace.h |  3 ++-
 2 files changed, 10 insertions(+), 15 deletions(-)

diff --git a/src/multipart-replace.c b/src/multipart-replace.c
index facca62..1f7a75c 100644
--- a/src/multipart-replace.c
+++ b/src/multipart-replace.c
@@ -127,7 +127,7 @@ int multipart_replace_reader(struct multipart_replace_stream *s, int fd, const c
 		struct frame *tmp = s->front;
 		s->front = s->back;
 		s->back = tmp;
-		s->framecount++;
+		pthread_cond_broadcast(&s->newframe);
 		pthread_rwlock_unlock(&s->frontlock);
 	}
  end:
@@ -141,17 +141,17 @@ int multipart_replace_writer(struct multipart_replace_stream *s, int fd, const c
 	int ret = 0;
 	FILE *stream = fdopen(fd, "w");
 	struct frame myframe = { 0 };
-	long lastframe = 0;
 	char *boundary = boundary_line(_boundary);
 	size_t boundary_len = strlen(boundary);
 
-	pthread_rwlock_rdlock(&s->frontlock);
 	while (running) {
+		pthread_cond_wait(&s->newframe, &s->newframe_lock);
+
 		/* get the most recent frame (copy `s->front` to `myframe`) */
+		pthread_rwlock_rdlock(&s->frontlock);
 		if (myframe.cap < (size_t)s->front->len)
 			myframe.buf = xrealloc(myframe.buf, myframe.cap = s->front->len);
 		memcpy(myframe.buf, s->front->buf, myframe.len = s->front->len);
-		lastframe = s->framecount;
 
 		pthread_rwlock_unlock(&s->frontlock);
 
@@ -166,16 +166,7 @@ int multipart_replace_writer(struct multipart_replace_stream *s, int fd, const c
 				stdioerror(stream, "dst <- nl");
 			fflush(stream);
 		}
-
-		/* poll until there's a new frame */
-		pthread_rwlock_rdlock(&s->frontlock);
-		while (s->framecount == lastframe && running) {
-			pthread_rwlock_unlock(&s->frontlock);
-			usleep(30000); /* a bit over 30 FPS */
-			pthread_rwlock_rdlock(&s->frontlock);
-		}
 	}
-	pthread_rwlock_unlock(&s->frontlock);
  end:
 	free(boundary);
 	free(myframe.buf);
@@ -189,11 +180,14 @@ void init_multipart_replace_stream(struct multipart_replace_stream *s) {
 	s->front = &s->a;
 	s->back = &s->b;
 	pthread_rwlock_init(&s->frontlock, NULL);
-	s->framecount = 0;
+	pthread_cond_init(&s->newframe, NULL);
+	pthread_mutex_init(&s->newframe_lock, NULL);
 }
 
 void destroy_multipart_replace_stream(struct multipart_replace_stream *s) {
 	free(s->a.buf);
 	free(s->b.buf);
 	pthread_rwlock_destroy(&s->frontlock);
+	pthread_cond_destroy(&s->newframe);
+	pthread_mutex_destroy(&s->newframe_lock);
 }
diff --git a/src/multipart-replace.h b/src/multipart-replace.h
index e4cced0..d302c5f 100644
--- a/src/multipart-replace.h
+++ b/src/multipart-replace.h
@@ -31,7 +31,8 @@ struct multipart_replace_stream {
 	struct frame a, b;
 	struct frame *front, *back;
 	pthread_rwlock_t frontlock;
-	long framecount;
+	pthread_cond_t newframe;
+	pthread_mutex_t newframe_lock;
 };
 
 int multipart_replace_reader(struct multipart_replace_stream *s, int fd, const char *boundary);
-- 
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