Tcl Source Code

In the following script control eventually returns to p1, which sets
<code>$done</code> to <code>success</code>.  The fact that <code>$done1</code>
has a final value of <code>failure</code> shows that the attempt to yield back
to p1 failed, so how did control end up in p1 again?


<code><verbatim>
variable done
proc p0 {} {
	yield
	variable done0
	after 0 [list [namespace which c1]]
	vwait [namespace current]::done0
}


proc p1 {} {
	variable done0
	yield
	yieldto try "yieldto [list [info coroutine]]" on error {} "
		::set [list [namespace current]]::done1 failure
		::set [list [namespace current]]::done0 failure
	"
	set done0 success
}

coroutine c0 p0
coroutine c1 p1
after 1 [list [namespace which c0]]
vwait [namespace current]::done0
puts [list status $done0 $done1]
</verbatim></code>

<b>output:</b>

<verbatim>
status success failure
</verbatim>

If the script doesn't attempt the inner yieldto, and just sets the variables
instead, the result is different:

<code><verbatim>
variable done
proc p0 {} {
	yield
	variable done0
	after 0 [list [namespace which c1]]
	vwait [namespace current]::done0
}


proc p1 {} {
	variable done0
	yield
	yieldto try "
		::set [list [namespace current]]::done1 failure
		::set [list [namespace current]]::done0 failure
	"
	set done0 success
}

coroutine c0 p0
coroutine c1 p1
after 1 [list [namespace which c0]]
vwait [namespace current]::done0
puts [list status $done0 $done1]
</verbatim></code>

<b>output:</b>

<verbatim>
status failure failure
</verbatim>


So apparently in the first script the failure to yield back to c1 affects some
internal state and changes the outcome.

Test case added in [5cfdd6ee7b7f2099].

Duplicate of [f9800d52bd61f240].