[Python-Dev] PEP needed? Introducing Tcl objects (original) (raw)

Martin v. Loewis martin@v.loewis.de
19 Feb 2002 21:22:16 +0100

"Jeffrey Hobbs" <jeffh@ActiveState.com> writes:

IIRC, TclSetMaxBlockTime is a one-short call - it sets the next block time, not all block times. I'm sure there was a reason for this, but that was implemented before I was a core guy. Anyway, I think you just need to try:

- result = TclDoOneEvent(TCLDONTWAIT); + TclSetMaxBlockTime(&blocktime); + result = TclDoOneEvent(0); and see if that satisfies the need for responsiveness as well as not blocking.

Thanks, but that won't help. Tcl still performs a blocking select. Studying the Tcl source, it seems that the SetMaxBlockTime feature is broken in Tcl 8.3. DoOneEvent has

/*
 * If TCL_DONT_WAIT is set, be sure to poll rather than
 * blocking, otherwise reset the block time to infinity.
 */

if (flags & TCL_DONT_WAIT) {
    tsdPtr->blockTime.sec = 0;
    tsdPtr->blockTime.usec = 0;
    tsdPtr->blockTimeSet = 1;
} else {
    tsdPtr->blockTimeSet = 0;
}

So if TCL_DONT_WAIT is set, the blocktime is 0, otherwise, it is considered not set. It then goes on doing

if ((flags & TCL_DONT_WAIT) || tsdPtr->blockTimeSet) {
    timePtr = &tsdPtr->blockTime;
} else {
    timePtr = NULL;
}
result = Tcl_WaitForEvent(timePtr);

So if TCL_DONT_WAIT isn't set, it will block; if it is, it will busy-wait. Looks like we lose either way.

In-between, it invokes the setupProcs of each input source, so that they can set a maxblocktime, but I don't think _tkinter should hack itself into that process.

So I don't see a solution on the path of changing how Tcl invokes select.

About thread-safety: Is Tcl 8.3 thread-safe in its standard installation, so that we can just use it from multiple threads? If not, what is the compile-time check to determine whether it is thread-safe? If there is none, I really don't see a solution, and the Sleep must stay.

Regards, Martin