Re: [fpc-pascal] Best way to check SimpleIPC for messages

[noreply]

On 2017-05-16 04:55, Michael Schnell wrote:

On 16.05.2017 07:30, Michael Van Canneyt wrote:


select is basically what peekmessage does.


AFAIK "select()" (and - more versatile -  "poll()"  ) in Linux uses
an appropriate system call to wait on one of multiple events (i.e.
devices, including e.g. pipes, which might be used by IPC). (Despite
the name) it does not do any "busy wait" ("polling"). So it's can be
used (instead of waiting in a blocking read)  in a worker-thread of an
"application". It's perfectly useful in an program without a message
queue provided by LCL or the mse-library.



But can it be used without threads at all without locking the app up
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Re: [fpc-pascal] Best way to check SimpleIPC for messages

[Michael Schnell]

On 17.05.2017 07:08, nore...@z505.com wrote:
 what happens when the application is not idle, but sort of idle? 


A new Queue event also only is serviced when no other previous events 
are peresent hence when the application gets "idle".


I don't know when exactly "OnIdle" is called. It can't be in a closed 
loop otherwise any application would always use 100% CPU.


Hence "OnIdle" is bound to work with an even greater latency than a 
decent queue entry like TThread.Queue or Application.QueueAsyncCall.


-Michael
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Re: [fpc-pascal] Best way to check SimpleIPC for messages

[Michael Schnell]

On 16.05.2017 07:30, Michael Van Canneyt wrote:


select is basically what peekmessage does.

AFAIK "select()" (and - more versatile -  "poll()"  ) in Linux uses 
an appropriate system call to wait on one of multiple events (i.e. 
devices, including e.g. pipes, which might be used by IPC). (Despite the 
name) it does not do any "busy wait" ("polling"). So it's can be used 
(instead of waiting in a blocking read)  in a worker-thread of an 
"application". It's perfectly useful in an program without a message 
queue provided by LCL or the mse-library.


-Michael
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Re: [fpc-pascal] Best way to check SimpleIPC for messages

[Mattias Gaertner]

On Wed, 17 May 2017 01:50:32 -0500
nore...@z505.com wrote:

> On 2017-05-17 00:54, Sven Barth via fpc-pascal wrote:
> > OnIdle() is called when there is no more event waiting in the
> > widgetset's event queue, basically meaning that the application has
> > nothing better to do anyway. It has nothing to do with CPU usage.
> >   
> 
> That makes sense.
> And recursively what happens if you call an event, inside the onidle, 
> ...
> 
> Recursive nightmare, or not a problem?

Not a problem for the LCL, but it may be a problem for your application.

Mattias
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Re: [fpc-pascal] Best way to check SimpleIPC for messages

[noreply]

On 2017-05-17 00:54, Sven Barth via fpc-pascal wrote:

OnIdle() is called when there is no more event waiting in the
widgetset's event queue, basically meaning that the application has
nothing better to do anyway. It has nothing to do with CPU usage.



That makes sense.
And recursively what happens if you call an event, inside the onidle, 
...


Recursive nightmare, or not a problem?
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Re: [fpc-pascal] Best way to check SimpleIPC for messages

[Sven Barth via fpc-pascal]

Am 17.05.2017 07:08 schrieb :
>
> On 2017-05-15 04:36, Michael Schnell wrote:
>>
>> On 12.05.2017 16:37, Michael Van Canneyt wrote:
>>>
>>>
>>> Check manually. What else is left ? There is no message queue, so no
loop in which to check at regular basis.
>>>
>> For event processing in a not threaded project or in the main thread
>> of a threaded project you at best use the Event Queue provided by some
>> Infrastructure library (e.g. LCL or mse). IMHO, SimpleIPC might makes
>> sense, if you don't want to use one of those. (mse and an enhanced
>> NoGui LCL "Widget Type", I have done a working draft for, can provide
>> a message queue even with no binding to a GUI Widget Set).
>>
>
> Isn't that what the application onidle is for, a way to check messages
using the application code in the LCL
>
> But a question is (sorry I am not familiar with "onidle"), what happens
when the application is not idle, but sort of idle? What classifies an idle
state? i.e. what if the cpu is at 3 percent consumption, or 55 percent, or
2 percent? What classifies an onidle? this documented somewhere?
> Is onidle reliable or hit and miss where the app is not idle enough, in
some cases?

OnIdle() is called when there is no more event waiting in the widgetset's
event queue, basically meaning that the application has nothing better to
do anyway. It has nothing to do with CPU usage.

Regards,
Sven
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Re: [fpc-pascal] Best way to check SimpleIPC for messages

[Michael Schnell]

On 12.05.2017 16:37, Michael Van Canneyt wrote:


Check manually. What else is left ? There is no message queue, so no 
loop in which to check at regular basis.


For event processing in a not threaded project or in the main thread of 
a threaded project you at best use the Event Queue provided by some 
Infrastructure library (e.g. LCL or mse). IMHO, SimpleIPC might makes 
sense, if you don't want to use one of those. (mse and an enhanced NoGui 
LCL "Widget Type", I have done a working draft for, can provide a 
message queue even with no binding to a GUI Widget Set).


But when using SimpleIPC for signaling to another process (executable, 
e.g.  a Lazarus "Application" ) I suppose, you  need a thread to avoid 
latency and/or huge CPU demand by polling to transfer the event to the 
Main Thread via the Event Queue (e.g. by Application.QueueAsyncCall or 
TTherad.Queue).


-Michael
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Re: [fpc-pascal] Best way to check SimpleIPC for messages

[Michael Van Canneyt]

On Mon, 15 May 2017, nore...@z505.com wrote:


On 2017-05-12 09:37, Michael Van Canneyt wrote:
Obviously "avoid threads where possible" but only if there is a 
simpler mechanism not reinventing a thread. So it seems to me onidle 
in fpgui is a simpler way than creating a new separate thread 
yourself, but how to do it in a program that has no fpgui onidle?


Check manually. What else is left ? There is no message queue, so no
loop in which to check at regular basis.



What's left is possibly something like apache 1.3 source code which 
somehow, AFAIR avoids using threads by using some other obscure strange 
thing, which I have forgotten. Possibly something like old dos programs 
used (sorry, not a Dos programmer, don't know.. not old enough).


They use select (or poll) and fork. So the equivalent of threads.
mpm = multi process module.

select is basically what peekmessage does.

Michael.
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Re: [fpc-pascal] Best way to check SimpleIPC for messages

[noreply]

On 2017-05-12 09:37, Michael Van Canneyt wrote:
Obviously "avoid threads where possible" but only if there is a 
simpler mechanism not reinventing a thread. So it seems to me onidle 
in fpgui is a simpler way than creating a new separate thread 
yourself, but how to do it in a program that has no fpgui onidle?


Check manually. What else is left ? There is no message queue, so no
loop in which to check at regular basis.



What's left is possibly something like apache 1.3 source code which 
somehow, AFAIR avoids using threads by using some other obscure strange 
thing, which I have forgotten. Possibly something like old dos programs 
used (sorry, not a Dos programmer, don't know.. not old enough).


Quote from some slashdot comment:
"There is an Apache2 mpm, called "prefork", which isn't threaded and 
basically makes Apache2 look like Apache1. But hey, we have a very good 
server already that looks like Apache1."


Some people have magically figured out how to avoid threads using 
possibly bizarre techniques..


Quote " It handles requests in a manner similar to Apache 1.3. It is 
appropriate for sites that need to avoid threading for compatibility 
with non-thread-safe libraries. It is also the best MPM for isolating 
each request, so that a problem with a single request will not affect 
any other."


I looked into the apache 1.3 sources before to figure out what they 
used, but long forgotten now.

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Re: [fpc-pascal] Best way to check SimpleIPC for messages

[Michael Van Canneyt]

On Fri, 12 May 2017, nore...@z505.com wrote:

Is the best general way to check IPC messages in SimpleIPC to spawn a 
thread? and check


I noticed in fpgui sample apps that use simpleipc, graemeg checks the 
messages in the fpgui OnIdle event, AFAICT, not a separate thread. But 
what if you are running a console mode program that has no onidle event?


Obviously "avoid threads where possible" but only if there is a simpler 
mechanism not reinventing a thread. So it seems to me onidle in fpgui is 
a simpler way than creating a new separate thread yourself, but how to 
do it in a program that has no fpgui onidle?


Check manually. What else is left ? 
There is no message queue, so no loop in which to check at regular basis.


On that note what would a lazarus app generally do to check for 
messages, without locking the app up? A similar OnIdle solution?


Yes. The sample programs check in Application.OnIdle.

Michael.
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