ringbuf: add thread-safe, thread-specific reset functions

This will allow both the reader and writer threads to
reset the ringbuffer in a thread-safe fashion.

git-svn-id: https://svn.musicpd.org/mpd/trunk@7390 09075e82-0dd4-0310-85a5-a0d7c8717e4f

src/ringbuf.c

@@ -62,6 +62,18 @@ void ringbuf_reset(struct ringbuf * rb)
 	rb->write_ptr = 0;
 }
 
+/* Reset the read and write pointers, thread-safe iff called only by writer */
+void ringbuf_writer_reset(struct ringbuf * rb)
+{
+	rb->write_ptr = rb->read_ptr;
+}
+
+/* Reset the read and write pointers, thread-safe iff called only by reader */
+void ringbuf_reader_reset(struct ringbuf * rb)
+{
+	rb->read_ptr = rb->write_ptr;
+}
+
 /*
  * Return the number of bytes available for reading.  This is the
  * number of bytes in front of the read pointer and behind the write

src/ringbuf.h

@@ -172,6 +172,24 @@ size_t ringbuf_read_space(const struct ringbuf * rb);
  */
 void ringbuf_reset(struct ringbuf * rb);
 
+/**
+ * Reset the write pointer to the read pointer, making an empty buffer.
+ *
+ * This should only be called by the writer
+ *
+ * @param rb a pointer to the ringbuffer structure.
+ */
+void ringbuf_writer_reset(struct ringbuf * rb);
+
+/**
+ * Reset the read pointer to the write pointer, making an empty buffer.
+ *
+ * This should only be called by the reader
+ *
+ * @param rb a pointer to the ringbuffer structure.
+ */
+void ringbuf_reader_reset(struct ringbuf * rb);
+
 /**
  * Write data into the ringbuffer.
  *