Tcl Source Code

Patch that implements a forthcoming TIP, entitled
"Script cancellation with Tcl_CancelEval" or something
similar.

Please test.  I would like to get some feedback on this
patch so that any necessary changes can be made prior
to writing the formal TIP.

Just tested the attached ZIP file.  It opens and validates OK.

I can try to find the patch and re-upload it; however, the functionality is already present in HEAD.

The tip285_v18.zip file looks broken. Can you upload again?

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Updated and committed to HEAD.

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File Added - 277953: tip285_v18.zip

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Updated, fixes to tests.

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File Added - 277853: tip285_v17.zip

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Updated to HEAD.  Minor enhancements and fixes.

File Added: tip285_v17.zip

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File Added - 276288: script_cancellation_16.zip

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Updated CANCELED interp flag to not use the previously used 0x10 value.

File Added: script_cancellation_16.zip

File Added - 273326: tk_cancellation_1.zip

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Adding preliminary patch for Tk changes.

File Added: tk_cancellation_1.zip

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File Added - 273323: script_cancellation_15.zip

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More minor corrections.

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File Added - 273267: script_cancellation_14.zip

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Minor corrections.

File Added: script_cancellation_14.zip

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File Added - 273192: script_cancellation_13.zip

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Patch updated.

Changed [cancel] to [interp cancel] and added appropriate docs.

File Added: script_cancellation_13.zip

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File Added - 273175: script_cancellation_12.zip

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Patch updated to latest HEAD.  

Still need to change [cancel] to [interp cancel] and add docs for it.

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Patch needs to be updated for latest HEAD.  Also, the plan is to change the script visible command to [interp cancel] instead of [cancel].

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File Added - 238301: script_cancellation_11.zip

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Updated (v11) patch to latest HEAD.

File Added: script_cancellation_11.zip

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File Added - 198625: script_cancellation_10.zip

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New v10 patch, various adjustments, corrected whitespace.

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File Added - 198366: script_cancellation_9.zip

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New v9 patch.  More cleanup and consistency fixes, now
complete with tests.  Docs for Tcl_Canceled and
Tcl_CancelEval complete.  Still working on [cancel] docs. 
TIP has been submitted and should be forthcoming.

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Sorry, I'm still working on the TIP, man pages, and tests.  

In the meantime, the code fully works.  The basic
functionality provided is the ability to cancel a script
running in an interpreter from any thread in the process via
Tcl_CancelEval or from within the interpreter itself via the
[cancel] command.  Some examples are provided below.

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An almost 1500 loc patch without a spec, man page or tests.
I'm not up to guessing what it is supposed to do, sorry.
When the forthcoming tip does come forth, I'll take a look.

File Added - 197788: script_cancellation8.zip

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Latest patch is against HEAD and cleans up a few things.

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A new patch revision is forthcoming...

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File Added - 184503: script_cancellation_7.zip

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Refreshed v6 patch against current HEAD (now v7).

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File Added - 182033: script_cancellation_6.zip

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Refactored error message handling to be simpler and more
robust (v6).

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File Added - 181487: script_cancellation_5.zip

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Updated (v5) patch supports a custom error message for
script cancellation via Tcl_CancelEval and [cancel].  Also
corrected mutex locking issue with CancelEvalProc.

Here is a quick Tk example of [cancel] usage:

----------------------------------------------------

package require Tk

pack [text .clock] -side top -expand true \
        -fill both -padx 10 -pady 10
                   
pack [button .go -padx 10 -pady 10 -text "Go" \
        -command [list goButton]] \
        -side left -padx 10 -pady 10
pack [button .cancel -padx 10 -pady 10 -text "Cancel" \
        -command [list cancelButton "clock stopped."]] \
        -side right -padx 10 -pady 10

proc goButton {args} {
  while {1} {
    catch {.clock delete 1.0 end}
    .clock insert end [clock format [clock seconds]]
    update
  }
}

proc cancelButton {msg} {
  cancel -unwind {} $msg
}

File Added - 181375: script_cancellation_4.zip

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The v4 patch is basically code complete.  However, I'm still
working on the documentation and test cases for [cancel].

Quite a lot of fine tuning has been done to both the new
code and the comments.  The Tcl_CancelEval function now
accepts a new flag TCL_CANCEL_UNWIND that allows the
evaluation stack for the target interpreter to be completely
unwound in the event of the pathological test cases like:

while {1} { catch { while {1} {incr x} } }

Here are some other test cases that work correctly with the
v4 patch:

# Tcl_CancelEval after delay test
# returns TCL_ERROR "eval cancelled" or "eval unwound" 
# based on flags passed to Tcl_CancelEval
after 30000

----------------------------------------------------------

# Tcl_CancelEval vwait test
# returns TCL_ERROR "eval cancelled" or "eval unwound" 
# based on flags passed to Tcl_CancelEval
vwait forever

----------------------------------------------------------

# Tcl_CancelEval very tight loop test
# returns TCL_ERROR "eval cancelled" or "eval unwound" 
# based on flags passed to Tcl_CancelEval
while {1} {}

----------------------------------------------------------

# Tcl_CancelEval tight loop with body test
# returns TCL_ERROR "eval cancelled" or "eval unwound" 
# based on flags passed to Tcl_CancelEval
while {1} {incr x}

----------------------------------------------------------

# Tcl_CancelEval with TCL_CANCEL_UNWIND test.
# This can only be cancelled if the TCL_CANCEL_UNWIND
# flag is used with Tcl_CancelEval.  It will return 
# TCL_ERROR "eval unwound" in that case.
while {1} { catch { while {1} {incr x} } }

----------------------------------------------------------

# Tcl_CancelEval with TCL_CANCEL_UNWIND slightly more 
# pathological unwind test
# returns TCL_ERROR "eval unwound" 
while {1} {
  catch { 
    while {1} {
      catch { 
        while {1} {incr x}
      } 
    } 
  } 
}

----------------------------------------------------------

# Tcl_CancelEval slave interp test
# returns TCL_ERROR "eval cancelled" or "eval unwound" 
# based on flags passed to Tcl_CancelEval
interp create foo; foo eval { while {1} {incr x} }

----------------------------------------------------------

# Tcl_CancelEval [subst] test
# returns TCL_ERROR "eval cancelled" or "eval unwound" 
# based on flags passed to Tcl_CancelEval
subst {[while {1} {incr x}]}

----------------------------------------------------------

# Tcl_CancelEval with TCL_CANCEL_UNWIND pathological slave 
# interp test
# returns TCL_ERROR "eval unwound"
interp create foo; foo eval {
  while {1} {
    catch { 
      while {1} { 
        catch { 
          while {1} {incr x}
        }
      }
    } 
  } 
}

----------------------------------------------------------

# basic [cancel] test
# returns TCL_ERROR "eval cancelled"
cancel

----------------------------------------------------------

# basic [cancel] test with "--"
# returns TCL_ERROR "eval cancelled"
cancel --

----------------------------------------------------------

# basic [cancel -unwind] test
# returns TCL_ERROR "eval unwound"
cancel -unwind --

----------------------------------------------------------

# [cancel] test
# returns TCL_ERROR "eval cancelled"
catch {unset foo i}
while {1} {
  incr i; lappend foo $i
  # pretend this is some complex 
  # logic or Tk button command.
  if {$i > 3} then {cancel} 
}

----------------------------------------------------------

# [cancel -unwind] test
# returns TCL_ERROR "eval unwound"
catch {unset foo i}
while {1} { 
  catch { 
    while {1} { 
      incr i; lappend foo $i
      # pretend this is some complex 
      # logic or Tk button command.
      if {$i > 3} then {cancel -unwind} 
    }
  } 
}

----------------------------------------------------------

# recursion test
# returns TCL_ERROR "eval cancelled"
proc foo { i } {
  if {$i > 10} then { 
    cancel 
  } else {
    return [foo [expr {$i + 1}]] 
  }
}; foo 0

File Added - 181083: script_cancellation_3.zip

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Attaching updated (v3) patch that works around the
Tcl_GetMaster (bug #1502071) issue.

The previous (v2) patch demonstrates the issue.

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NOTE: This patch needs to be reviewed by kennykb and msofer.

File Added - 180714: script_cancellation_2.zip

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Fixed interp deletion issue, slave interp support, and some
issues with commands that block (after, vwait).  Tweaked docs.

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