Smalltalk › Pharo › Pharo Smalltalk Developers

Interrupting processes question. Can method return be interrupted?

_‹ Previous Topic Next Topic _›

Classic

List

Threaded

3 messages Options

Denis Kudriashov

Interrupting processes question. Can method return be interrupted?

Look at example:

methodA
| result |
result := false.
[result := self methodB] ensure: [result ifTrue: [...]]

methodB
result := 1 < 2.

^result

Imagine now that methodB starts execution in context of call inside methodA.

Is it possible to terminate process at point of methodB return (^result)?

In that case ensure block in methodA will perform wrong logic.

Eliot Miranda-2

Re: Interrupting processes question. Can method return be interrupted?

Hi Denis,

On Thu, Jan 7, 2016 at 7:54 AM, Denis Kudriashov <[hidden email]> wrote:

Look at example:

methodA
| result |
result := false.
[result := self methodB] ensure: [result ifTrue: [...]]

methodB
result := 1 < 2.
^result

Imagine now that methodB starts execution in context of call inside methodA.
Is it possible to terminate process at point of methodB return (^result)?
In that case ensure block in methodA will perform wrong logic.

Returns are not suspension points, so no. In the Cog and Stack VMs the only suspension points are backward jumps (at the end of while loops) and method activations. Note that invocations of methods with primitives (including quick methods, e.g. ^true or ^instVar) are not suspension points, unless their primitives fail, or unless the primitives are suspend, wait et al.

In the interpreter VM (incorrectly IMO) primitive invocation in the context of a perform:, tryPrimitive:, executeMethod: primitive is also a suspension point. i.e. /any/ primitive including a quick primitive invoked via primitives 83, 84, 100, 188, 188 & 189, could potentially be a suspension point, in which case the process would be suspended immediately following the send that invoked the primitive.

_,,,^..^,,,_

best, Eliot

Eliot Miranda-2

Re: Interrupting processes question. Can method return be interrupted?

Hi Denis,

On Thu, Jan 7, 2016 at 8:44 AM, Eliot Miranda <[hidden email]> wrote:

Hi Denis,

On Thu, Jan 7, 2016 at 7:54 AM, Denis Kudriashov <[hidden email]> wrote:
Look at example:

methodA
| result |
result := false.
[result := self methodB] ensure: [result ifTrue: [...]]

methodB
result := 1 < 2.
^result

Imagine now that methodB starts execution in context of call inside methodA.
Is it possible to terminate process at point of methodB return (^result)?
In that case ensure block in methodA will perform wrong logic.

Returns are not suspension points, so no. In the Cog and Stack VMs the only suspension points are backward jumps (at the end of while loops) and method activations. Note that invocations of methods with primitives (including quick methods, e.g. ^true or ^instVar) are not suspension points, unless their primitives fail, or unless the primitives are suspend, wait et al.

I forgot to say that block activations are also suspension points. In the Cog JIT sufficiently simple methods and sufficiently simple blocks are not necessarily suspension points when converted to machine code. the KIT will generate a frameless method (which is not a suspension point) if the block or method contains only #== and #class sends and no jumps and no temporary accesses. But this is just an optimization, and it removes suspension points not adds them.

In the interpreter VM (incorrectly IMO) primitive invocation in the context of a perform:, tryPrimitive:, executeMethod: primitive is also a suspension point. i.e. /any/ primitive including a quick primitive invoked via primitives 83, 84, 100, 188, 188 & 189, could potentially be a suspension point, in which case the process would be suspended immediately following the send that invoked the primitive.

_,,,^..^,,,_
best, Eliot

_,,,^..^,,,_

best, Eliot