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Quiz #4 [message #57802]

Sat, 18 December 2021 09:21

mirek
Messages: 14265
Registered: November 2005

Ultimate Member

Now for something much more fun:

CONSOLE_APP_MAIN
{
	int x = 0;
	CoDo([&] {
		CoWork::FinLock();
		x++;
	});
	DDUMP(x);
}

What can you say about the number printed to the log?

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Re: Quiz #4 [message #57803 is a reply to message #57802]

Sat, 18 December 2021 10:24

Oblivion
Messages: 1214
Registered: August 2007

Senior Contributor

Quote:

Now for something much more fun:

CONSOLE_APP_MAIN
{
int x = 0;
CoDo([&] {
CoWork::FinLock();
x++;
});
DDUMP(x);
}

What can you say about the number printed to the log?

Ideally it should be 1.

But in this case the result should (or expected to) be "0 < x <= INT_MAX", depending on the underlying hardware/OS task/process scheduling?

Best regards,
Oblivion

Github page: https://github.com/ismail-yilmaz
Bobcat the terminal emulator: https://github.com/ismail-yilmaz/Bobcat

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Re: Quiz #4 [message #57804 is a reply to message #57803]

Sat, 18 December 2021 14:08

mirek
Messages: 14265
Registered: November 2005

Ultimate Member

Oblivion wrote on Sat, 18 December 2021 10:24

Quote:
Now for something much more fun:

CONSOLE_APP_MAIN
{
int x = 0;
CoDo([&] {
CoWork::FinLock();
x++;
});
DDUMP(x);
}

What can you say about the number printed to the log?

Ideally it should be 1.

But in this case the result should (or expected to) be "0 < x <= INT_MAX", depending on the underlying hardware/OS task/process scheduling?

Best regards,
Oblivion

Incorrect.

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Re: Quiz #4 [message #57810 is a reply to message #57804]

Sat, 18 December 2021 21:21

Oblivion
Messages: 1214
Registered: August 2007

Senior Contributor

OK. What am I missing here?

AFAIK,

- CoDo() function is blocking, i.e. it will wait for the threads to join, before it exits.
- CoDo() calls CoWork::Loop(). The API document states that:

Schedules fn to be run on all worker threads and on calling thread. After the first thread returns from fn, all other scheduled fn jobs that has not started yet are unscheduled. Waits for all started jobs to finish.

Best regards,
Oblivion

Github page: https://github.com/ismail-yilmaz
Bobcat the terminal emulator: https://github.com/ismail-yilmaz/Bobcat

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Re: Quiz #4 [message #57811 is a reply to message #57810]

Sun, 19 December 2021 09:28

mirek
Messages: 14265
Registered: November 2005

Ultimate Member

You are not completely wrong.

1 really is the most probable result with current implementation. This is basically pure race condition - how many worker threads will CoDo unblock until it registers that first of them finished.

Anyway, INT_MAX is definitely a little bit high - the teoretical maximum is the number of worker threads.

Mirek

[Updated on: Sun, 19 December 2021 09:29]

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