merge some select calls for splice users

Avoid an additional select syscall in the splice path by injecting
the target checks into the main loop.  We can do this because we
always process writers before readers.  This adds additional
userspace processing, but it avoids one potentially expensive (and
potentially task-switching) syscall in many cases; so it should be
worth it to avoid skipping with small buffer.

This should avoid buffer underuns with mixed-sized buffers when
using multiple sinks.

This could work for the read_write path, too, but I don't
use that enough and this change may still be buggy even
for splice users.

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/dtas/player.rb b/lib/dtas/player.rb
index 56fbdac..04c03b0 100644
--- a/lib/dtas/player.rb
+++ b/lib/dtas/player.rb
@@ -300,6 +300,13 @@ class DTAS::Player # :nodoc:
     end
   end
 
+  def _optimize_write_prepare(targets)
+    targets.each do |dst|
+      dst.wait_writable_prepare
+      @srv.wait_ctl(dst, :wait_writable)
+    end
+  end
+
   # returns a wait_ctl arg for self
   def broadcast_iter(buf, targets)
     case rv = buf.broadcast(targets)
@@ -315,6 +322,7 @@ class DTAS::Player # :nodoc:
       # via DTAS::Sink#writable_iter
       :ignore
     else # :wait_readable or nil
+      _optimize_write_prepare(targets)
       rv
     end
   end