Amend token_bucket_rw_dec to indicate which buckets became empty.

src/common/token_bucket.c

@@ -238,13 +238,18 @@ token_bucket_rw_dec_write(token_bucket_rw_t *bucket,
 
 /**
  * As token_bucket_rw_dec_read and token_bucket_rw_dec_write, in a single
- * operation.
+ * operation.  Return a bitmask of TB_READ and TB_WRITE to indicate
+ * which buckets became empty.
  */
-void
+int
 token_bucket_rw_dec(token_bucket_rw_t *bucket,
                     ssize_t n_read, ssize_t n_written)
 {
-  token_bucket_rw_dec_read(bucket, n_read);
-  token_bucket_rw_dec_write(bucket, n_written);
+  int flags = 0;
+  if (token_bucket_rw_dec_read(bucket, n_read))
+    flags |= TB_READ;
+  if (token_bucket_rw_dec_write(bucket, n_written))
+    flags |= TB_WRITE;
+  return flags;
 }
 

src/common/token_bucket.h

@@ -85,8 +85,8 @@ int token_bucket_rw_dec_read(token_bucket_rw_t *bucket,
 int token_bucket_rw_dec_write(token_bucket_rw_t *bucket,
                               ssize_t n);
 
-void token_bucket_rw_dec(token_bucket_rw_t *bucket,
-                         ssize_t n_read, ssize_t n_written);
+int token_bucket_rw_dec(token_bucket_rw_t *bucket,
+                        ssize_t n_read, ssize_t n_written);
 
 static inline size_t token_bucket_rw_get_read(const token_bucket_rw_t *bucket);
 static inline size_t