xz: Fix semi-busy-waiting in xz --flush-timeout.

When input blocked, xz --flush-timeout=1 would wake up every
millisecond and initiate flushing which would have nothing to
flush and thus would just waste CPU time. The fix disables the
timeout when no input has been seen since the previous flush.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/xz/file_io.h b/src/xz/file_io.h
index 32dcad0c..3989c701 100644
--- a/src/xz/file_io.h
+++ b/src/xz/file_io.h
@@ -49,6 +49,10 @@ typedef struct {
 	/// True once end of the source file has been detected.
 	bool src_eof;
 
+	/// For --flush-timeout: True if at least one byte has been read
+	/// since the previous flush or the start of the file.
+	bool src_has_seen_input;
+
 	/// If true, we look for long chunks of zeros and try to create
 	/// a sparse file.
 	bool dest_try_sparse;