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Editorial Team
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Asked: 2026-06-17T21:59:34+00:00

Does Tcl do any internal input buffering that’s out of the script writers control?

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Does Tcl do any internal input buffering that’s out of the script writers control? Will the following code possibly waste entropy (read more than 1 byte), and if so, how can I prevent it?

set stream [open "/dev/srandom"]
chan configure $stream -translation binary
set randomByte [chan read $stream 1]
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1 Answer

  1. Editorial Team

    Yes, tcl defaults to buffering and will waste enthropy (as much as a single read call will decide to hand over).

    I thought that you can prevent it with

    chan configure $stream -buffering none

    But no, -buffering has no effect on input queue (it’s not a single buffer internally).

    However,

    chan configure $stream -buffersize 0

    does the trick, as I’ve seen from an experiment with stdin under strace. It makes any input go in reads (syscall) of size 1 (an argument to TCL read doesn’t matter), so it would be extremely slow for normal use.

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