read       |   xform       |  write
thread      |  thread       |  thread
------------|---------------|---------------   
Issue read  | wait lock(in) | wait lock(out)
IO wait     |               |               
            |               |               
--------------------------------------------
            |               |               
            ~               ~              
 some unknown number of kernel task switches
            ~               ~              
            |               |               
----------------------------------------------
Read completes     "        |  wait lock(out)
signal record               |               
issue next read             |               
IO wait     |  wait lock(in)|               
--------------------------------------------
            |               |               
            ~               ~              
 some unknown number of kernel task switches
            ~               ~              
            |               |               
----------------------------------------------
 IOwait     |obtain lock(in)|  wait lock(out)
            | do stuff      |               
            | do stuff      |               
            | wait lock(out)|
            | signal write  |               
            | loop
--------------------------------------------
            |               |               
            ~               ~              
 some unknown number of kernel task switches
            ~               ~              
            |               |               
----------------------------------------------
            | wait lock(in) | obtain lock(out)
            |               | write out     
            |               | IO wait       
            |               |               
            |               |