MINOR: debug: split ha_thread_dump() in two parts

We want to have a function to trigger the dump and another one to wait
for it to be completed. This will be important to permit panic dumps to
be done on local threads. For now this does not change anything, as the
function still calls the two new functions one after the other.

Author: wtarreau

src/debug.c

@@ -354,9 +354,11 @@ void ha_thread_dump_one(int thr, int from_signal)
  * current thread or if thread dump signals are not implemented, or by sending
  * a signal if it's a remote one and the feature is supported. The buffer <buf>
  * will get the dump appended, and the caller is responsible for making sure
- * there is enough room otherwise some contents will be truncated.
+ * there is enough room otherwise some contents will be truncated. The function
+ * waits for the called thread to fill the buffer before returning. It does not
+ * release the called thread yet.
  */
-void ha_thread_dump(struct buffer *buf, int thr)
+void ha_thread_dump_fill(struct buffer *buf, int thr)
 {
 	struct buffer *old = NULL;
 
@@ -379,14 +381,37 @@ void ha_thread_dump(struct buffer *buf, int thr)
 #endif
 		ha_thread_dump_one(thr, thr != tid);
 
+	/* now wait for the dump to be done */
+	while (HA_ATOMIC_LOAD(&ha_thread_ctx[thr].thread_dump_buffer) != (void*)0x1UL)
+		ha_thread_relax();
+}
+
+/* Indicates to the called thread that the dumped data are collected. It waits
+ * for the dump to be completed if it was not the case.
+ */
+void ha_thread_dump_done(struct buffer *buf, int thr)
+{
+	struct buffer *old;
+
 	/* now wait for the dump to be done, and release it */
 	do {
-		if (old)
+		old = HA_ATOMIC_LOAD(&ha_thread_ctx[thr].thread_dump_buffer);
+		if (old != (void*)0x1UL) {
 			ha_thread_relax();
-		old = (void*)0x01;
+			continue;
+		}
 	} while (!HA_ATOMIC_CAS(&ha_thread_ctx[thr].thread_dump_buffer, &old, 0));
 }
 
+/* performs a complete thread dump: calls the remote thread and marks the
+ * buffer as read.
+ */
+void ha_thread_dump(struct buffer *buf, int thr)
+{
+	ha_thread_dump_fill(buf, thr);
+	ha_thread_dump_done(buf, thr);
+}
+
 /* dumps into the buffer some information related to task <task> (which may
  * either be a task or a tasklet, and prepend each line except the first one
  * with <pfx>. The buffer is only appended and the first output starts by the