I'd like to draw (pen and pencils) threads interaction in a UML(-like) notation. I don't insist on UML, anything that is obvious to the reader should do.
I started with sequence diagrams, but I don't feel this is the best way to do that. All the time, there would be "action initiators" coming from off-screen which kinda break the SSD idea. I inherited a medium size code base with around 9 - 10 threads each owning a state machine and I'm trying to figure out how it works.
How should I visualize thread interaction?