Creates a SignalSource that's dispatched when
condition is met
for the given
For example, if condition is IN, the source will be dispatched when there's data available for reading.
add_watch is a simpler interface to this same functionality, for the case where you want to add the source to the default main loop context at the default priority.
On Windows, polling a SignalSource created to watch a channel for a socket puts the socket in non-blocking mode. This is a side-effect of the implementation and unavoidable.
a IOChannel to watch
conditions to watch for
a new SignalSource