No, it's called testing many concurrent operations.

Implementing a complex concurrent algorithm based on your understanding of it, without proper testing is called luck, and often called delusion.

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teraflop 4 days ago | parent | next [-]

You can't easily, automatically test concurrent code for correctness without testing all possible interleavings of instructions, and that state space is usually galactically huge.

It is very easy to write multithreaded code that is incorrect (buggy), but where the window of time for the incorrectness to manifest is only a few CPU instructions at a time, sprinkled occasionally throughout the flow of execution.

Such a bug is unlikely to be found by test cases in a short period of time, even if you have 1000 concurrent threads running. And yet it'll show up in production eventually if you keep running the code long enough. And of course, when it does show up, you won't be able to reproduce it.

That is, I think, what the parent commenter means by "luck".

This is similar to the problem you'll run into when testing code that explicitly uses randomness. If you have a program that calls rand(), and it works perfectly almost all the time but fails when rand() returns the specific number 12345678, and you don't know ahead of time to test that value, then your automated test suite is unlikely to ever catch the problem. And testing all possible return values of rand() is usually impractical.

	▲	nick__m 4 days ago \| parent \| next [-]
		There is a cost benefit ratio and context that matters. The repeat the concurent operations 1000times technique is adequate for a CRUD API but it's whofully inadequate for a database engine or garbage collector.
	▲	wubrr 4 days ago \| parent \| prev \| next [-]
		It will obviously not catch all bugs. Nothing will. But it is a relatively easy and reliable way to catch many of them. It works.
	▲	nijave 3 days ago \| parent \| prev \| next [-]
		There's still value in eliminating ways your program can wrong even if you can't eliminate all of them. Using your logic, why bother testing at all.
	▲	afiori 4 days ago \| parent \| prev [-]
		and if you have too many threads running you could have slowdowns in the system that prevent the race condition from happening

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JackSlateur 4 days ago | parent | prev [-]

What algorithm ? The whole idea is that algorithms are useless, and you should just write a bunch of tests and go with it

Yes, if I write stuff with locks, I shall ensure that my code acquires and releases locks correctly

This is completely off-topic with the original post;

Also, you cannot prove something by tests; Just because you found 100000 cases where your code works does not mean there is not a case where is does not (just as you cannot prove that unicorn does not exist) :)

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sarchertech 4 days ago | parent | next [-]

> Also, you cannot prove something by tests; Just because you found 100000 cases where your code works does not mean there is not a case where is does not (just as you cannot prove that unicorn does not exist) :)

That’s exactly it. For any non trivial program, there exists an infinite number of ways your program can be wrong and still pass all your tests.

Unless you can literally test every possible input and every bit of state this holds true.

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wubrr 4 days ago | parent | next [-]

For any 'non trivial' program there exists an infinite number of ways your program can be wrong but you still believe it's right.

Testing is not a perfect solution to catch all bugs. It's a relatively easy, efficient and reliable way to catch many common bugs though.

	▲	sarchertech 2 days ago \| parent [-]
		Sure but it's not a reliable replacement for understanding what the program you wrote is doing either.

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pfdietz 4 days ago | parent | prev [-]

And yet, (1) testing finds bugs in any nontrivial program that hasn't been tested, and (2) test long enough and with enough variety and you can make programs significantly more reliable.

Perfect is the enemy of good, and absent academic fantasies of verified software testing is essential (even then, it's still essential, since you are unlikely to have verified every component of your system.)

	▲	sarchertech 2 days ago \| parent [-]
		Sure testing is useful. It's not so useful that you don't need to understand what you're doing though.

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wubrr 4 days ago | parent | prev [-]

It's not about making sure your system is 100% perfect. You cannot do that on any real sufficiently complex system. It's about testing the core functionality in a relatively straightforward and reliable way (including concurrency testing), to catch many common bugs.

	▲	JackSlateur 3 days ago \| parent [-]
		My shit is the backbone of a multibillions compagny Common bugs are not enough, uncommon bugs are just too expensive