Hacker News Reader

Comment by vvanders | Hacker News Reader

> typically not as general-purpose as print

In my domain which doesn't usually cover distributed systems printf can be worse because it introduces synchronization primitives that have caused race conditions to disappear(and that race condition causes second order heap corruption or the like). On one platform system memory was so small(8mb total) that each output to stdout went over the serial link slowing performance down to 1/20th of a realtime process under any real logging.

Like I said, different tools for different uses, and really depends on the context. If there was one size fits all then we'd just use that but the diversity of debugging tools I think shows that you need a variety of techniques to approach the problems we encounter.

View on HN

> Like I said, different tools for different uses, and really depends on the context

We totally agree, and I'm not sure what we're arguing about--perhaps you can fill me in.

I'm arguing that print is almost always worse than any specialized tool. (After all, who would use a specialized tool worse than print?) There is not a one-size-fits-all tool, and print is not a one-size-fits-all tool.

Indeed almost every seasoned developer has a story about print failing. Whether it's the mysterious "Heisenbug" that disappears when you measure it (like the sync issues you mention) -- my personal story is when I was trying to debug a (class project) kernel scheduler. Printing to the console was so slow that by the time I'd printed anything, the scheduler had moved on to the next time slice!

It's worth nothing that "print debugging" is not literally just using the "print" function; it's a style of debugging that involves logging specific information using some logging function (usually, but not always, print) and then analyzing it after the fact (usually, but not always, by reading the printed output).

This strategy of "get data out, then analyze it" is the general form of print debugging, and in the small-memory case, or the sync Heisenbug case, this often means collecting data in the appropriate variables before outputting it to be visible. Isn't this still print debugging, even though it doesn't use a "print" function?

I think we're mostly arguing about how useful the various approaches are. At least for me print debugging is a measure of last resort unless I want to extract some historical data out and I know it won't influence the timing of the issue I'm trying to chase down.

With print debugging your inserting the whole build + deploy + repro setup loop into your debugging, if that's a long time(say 20 minutes in one job I had with production hardware) you're in for a world of pain. I find that just about any other tool usually is an order of magnitude more efficient.

Also even the "step debugger" tools do the same thing you'd do with a print. LLVM for instance uses the IR JIT API to generate watch/eval values: https://releases.llvm.org/9.0.0/docs/ORCv2.html#use-cases

IMO you should relentlessly optimize your iteration times, that's the inner loop of development speed and print debugging fares pretty poorly in that area for all the reasons above.

> I think we're mostly arguing about how useful the various approaches are.

Ah, that's fair.

> At least for me print debugging is a measure of last resort

Right, and I think this depends on the domain. For lots of mature environments, this makes sense -- there's been years for tooling to catch up to the kinds of bugs people run into, possibly corporate money being put into developing debugging tools, etc.

> IMO you should relentlessly optimize your iteration times, that's the inner loop of development speed and[...]

Agreed, though the effect on print debugging on iteration time is very environment-dependent.

> [...]print debugging fares pretty poorly in that area for all the reasons above

Adding console.log to a web app can be a trivial change (though of course reproducing app state is another issue) -- again very environment-dependent.

Reply on news.ycombinator.com