[Xenomai-core] [PATCH] rtdk: Suspend/resume printer thread

[Jan Kiszka]

If someone is linking against rtdk for other reasons than using
rt_print, we should not let the printer thread poll the buffers
needlessly. So suspend it in case no buffer exists and resume once some
thread starts to use RT printing services.

Signed-off-by: Jan Kiszka <jan.kis...@siemens.com>
---

 src/rtdk/rt_print.c |   16 ++++++++++++++--
 1 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/rtdk/rt_print.c b/src/rtdk/rt_print.c
index 2d6875f..0615247 100644
--- a/src/rtdk/rt_print.c
+++ b/src/rtdk/rt_print.c
@@ -61,11 +61,13 @@ struct print_buffer {
 };
 
 static struct print_buffer *first_buffer;
+static int buffers;
 static uint32_t seq_no;
 static size_t default_buffer_size;
 static struct timespec print_period;
 static int auto_init;
 static pthread_mutex_t buffer_lock;
+static pthread_cond_t printer_wakeup;
 static pthread_key_t buffer_key;
 static pthread_t printer_thread;
 
@@ -258,6 +260,9 @@ int rt_print_init(size_t buffer_size, const char 
*buffer_name)
                first_buffer->prev = buffer;
        first_buffer = buffer;
 
+       buffers++;
+       pthread_cond_signal(&printer_wakeup);
+
        pthread_mutex_unlock(&buffer_lock);
 
        pthread_setspecific(buffer_key, buffer);
@@ -329,6 +334,8 @@ static void cleanup_buffer(struct print_buffer *buffer)
        if (next)
                next->prev = prev;
 
+       buffers--;
+
        pthread_mutex_unlock(&buffer_lock);
 
        free(buffer->ring);
@@ -397,13 +404,16 @@ static void print_buffers(void)
 static void *printer_loop(void *arg)
 {
        while (1) {
-               nanosleep(&print_period, NULL);
-
                pthread_mutex_lock(&buffer_lock);
 
+               while (buffers == 0)
+                       pthread_cond_wait(&printer_wakeup, &buffer_lock);
+
                print_buffers();
 
                pthread_mutex_unlock(&buffer_lock);
+
+               nanosleep(&print_period, NULL);
        }
 }
 
@@ -444,6 +454,8 @@ void __rt_print_init(void)
        pthread_mutex_init(&buffer_lock, NULL);
        pthread_key_create(&buffer_key, (void (*)(void*))cleanup_buffer);
 
+       pthread_cond_init(&printer_wakeup, NULL);
+
        pthread_attr_init(&thattr);
        pthread_attr_setstacksize(&thattr, PTHREAD_STACK_MIN);
        pthread_create(&printer_thread, &thattr, printer_loop, NULL);

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