til_fb: introduce til_fb_halt()

This makes it so til_fb_page_get() will return NULL when the fb
has been "halted".  If til_fb_page_get() is already waiting for a
page to become available, it will be woken up by til_fb_halt().

Preparatory commit for eliminating the reliance on
pthread_cancel() to terminate rototiller_thread() on shutdown.

Cancellation is always a PITA, especially cross-platform, but in
general it's so easy to have subtle bugs when using it.

2 files changed, 25 insertions, 2 deletions

diff --git a/src/til_fb.c b/src/til_fb.c
index 10a5931..1bdb2e7 100644
--- a/src/til_fb.c
+++ b/src/til_fb.c
@@ -143,6 +143,7 @@ typedef struct til_fb_t {
 	_til_fb_page_t		*all_pages_tail;
 
 	unsigned		put_pages_count;
+	unsigned		halted:1;
 } til_fb_t;
 
 #ifndef container_of
@@ -391,8 +392,14 @@ static inline _til_fb_page_t * _til_fb_page_get(til_fb_t *fb)
 	 * pages faster than vhz.
 	 */
 	pthread_mutex_lock(&fb->inactive_mutex);
-	while (!(page = fb->inactive_pages_tail))
+	while (!(page = fb->inactive_pages_tail) && !fb->halted)
 		pthread_cond_wait(&fb->inactive_cond, &fb->inactive_mutex);
+
+	if (!page) {
+		pthread_mutex_unlock(&fb->inactive_mutex);
+		return NULL;
+	}
+
 	fb->inactive_pages_tail = page->previous;
 	if (fb->inactive_pages_tail)
 		fb->inactive_pages_tail->next = NULL;
@@ -410,7 +417,13 @@ static inline _til_fb_page_t * _til_fb_page_get(til_fb_t *fb)
 /* public interface */
 til_fb_fragment_t * til_fb_page_get(til_fb_t *fb)
 {
-	return &(_til_fb_page_get(fb)->fragment.public);
+	_til_fb_page_t	*page;
+
+	page = _til_fb_page_get(fb);
+	if (!page)
+		return NULL;
+
+	return &page->fragment.public;
 }
 
 
@@ -602,6 +615,15 @@ void til_fb_rebuild(til_fb_t *fb)
 }
 
 
+void til_fb_halt(til_fb_t *fb)
+{
+	assert(fb);
+
+	fb->halted = 1;
+	pthread_cond_signal(&fb->inactive_cond);
+}
+
+
 /* accessor for getting the ops_context */
 void * til_fb_context(til_fb_t *fb)
 {
diff --git a/src/til_fb.h b/src/til_fb.h
index 1f100dd..5ad210f 100644
--- a/src/til_fb.h
+++ b/src/til_fb.h
@@ -55,6 +55,7 @@ til_fb_t * til_fb_free(til_fb_t *fb);
 void til_fb_get_put_pages_count(til_fb_t *fb, unsigned *count);
 int til_fb_new(const til_fb_ops_t *ops, const char *title, const til_setup_t *setup, int n_pages, til_fb_t **res_fb);
 void til_fb_rebuild(til_fb_t *fb);
+void til_fb_halt(til_fb_t *fb);
 void * til_fb_context(til_fb_t *fb);
 int til_fb_flip(til_fb_t *fb);
 void til_fb_fragment_divide(til_fb_fragment_t *fragment, unsigned n_fragments, til_fb_fragment_t fragments[]);