Garbage collection gets a bad rep from garbage collectors that are tuned for throughput rather than latency, but there is no lower limit to latency for garbage collection and there are GCs out there that prove it (like Azul). If you can afford dynamic memory allocation, you can afford garbage collection. And if you can't afford it, you can just preallocate and turn off the garbage collector.
This is 100% false. It's easy to configure Linux itself to only occupy 1 or 2 cores (one real + the hyper-thread for that real core), and then pin your own application threads to the other cores where no other code will run. This setup has identical application performance (other than not having those two Linux cores) to having no OS at all. 100% predictable, ZERO jitter application code (including user-space networking).
Except…you can still SSH in to your "no OS" Linux box, you have a file system, can run cron jobs, git, gdb, WireGuard, etc. So it's much, much better in practice and what actual high-performance network developers actually do.
Essentially no one has run a literal "no OS" box for at least a decade; everyone who is running on normal hardware does what I just described with Linux because the cost is dirt cheap and it's way too convenient.
As to "run of the mill software dev" this is not a snarky comment, this is just reality.
Most devs have absolutely no idea how to configure Linux at all, other than to make their application work. Not to mention configure for real time operation.
So I stand by my comment that comes from over two decades of experience in the field.
Hacker News is a site that values intellectual curiosity, not snark: you should have replied with an explanation of what you are actually doing to get that kind of thing out of the Linux kernel. What value is your experience in the field to this community if you refuse to share it with others? In this case my analogy is even stronger because you could argue that explaining imaginary numbers to a third grader may be difficult, but "I set CONFIG_whatever to this value and set the kernel to never schedule my application off this core" is exactly the kind of response that would be expected in this context.
Downvoting reasonable posts that do not fit somebody's point of view without providing any constructive explanations is of course way better.
It is my understanding that the other real time linux attempts ended up in similar territory, good but not sub 5 microsecond good.
Dev A "You should use X"
Dev B "We tried X, it was way to slow"
Dev A "You must be doing it wrong, I use X all the time and it's very fast"
This went back and forth like this for a good 15 minutes before they realized they where both getting the same performance, but just had a very different definition of "fast" and "slow".
Neither is software running in all your electronics.
All these require software that has some different requirements that typically are incompatible with unpredictability of a garbage collected dynamic language.
https://www.ptc.com/en/blogs/plm/ptc-perc-virtual-machine-te...
Better deflect that incoming missile on time before the next GC pause.
Aegis is built for defending against missiles going at most mach 4-5. Mach 5 is ~1700 m/s, so during a millisecond GC pause it will travel slightly under 2 meters. Ship-based SAMs will have proximity-fused fragmentation warheads and even back in the 70s those had a kill radius of >100m (see for example https://en.wikipedia.org/wiki/S-75_Dvina). So even a GC pause at the worst possible moment would not significantly impact the probability to hit the target. Even really fast things in the real world are really slow compared to computers.
(Of course, in practice the Aegis system will only provide midcourse corrections to the missile. The fuse and end phase guidance control software would not interface much with the rest of the combat management system anyway.)
The rockets close head on (so the speeds add together) and then the rocket trying to kill the other one explodes at right distance to the side of the other rocket, exploding in a cone of debris.
That cone of debris must intersect the other rocket at a right point. It can't just hit anywhere, to reliably kill it must hit a specific part of the other rocket.
So, realistically, you have to time your explosion to something like tens of microseconds.
Also getting there is a control loop problem and it requires very precise control. The more jitter in execution of the control loop the worse steering it will be and less chance it will get to the right place at the right time.
First of all, a SM-2 will not use the flight path you describe as they tend to "dive down" on a sea skimming missile. But even the shorter range Sea Sparrow missiles that do behave as you describe use multiple guidance phases. In the early and mid-phase guidance phases, the radar reflections from the target missile will not be strong enough for the relatively small receiver in the missile, so the system must depend on midcourse guidance updates (little bit to the right, little bit up, etc) from the combat management system on board the launching vessel to navigate to a "close enough" location from where the sensors on board the missile can acquire the target. The end-phase guidance and fuse timings are quite critical, as you say, but they are also not really under command of the CMS but rather done by embedded systems on board the missile. Generation of the mid-course guidance updates is not nearly as time critical and won't suffer much from a 1 ms pause. The error in location estimation of the target due to sensor imperfections (limited angular resolution, clock jitter, athmospheric effects, etc etc) will be way larger than the 2 meter from the GC pause.
I can't imagine a scenario in which an enemy would be able to saturate the defense system with a continuous onslaught that would make the system run out of memory. You'll sooner run out of SAMs and ammo for that fancy gun that's used to shoot down missiles at close range. And if the enemy can mount such an onslaught, then the ultimate GC will soon run anyway - all memory will be released when the ship sinks.
(I think back to that famous story of a missile with a memory leak, whose designers figured the missile will hit its target or run out of fuel faster than it'll run out of memory.)
But to answer your question, there are cases where the JVM is used without GC and it runs for a day, and gets restarted at night. Afaik some bank does it for some form of HFT.
https://devblogs.microsoft.com/oldnewthing/20180228-00/?p=98...
"[...] Since the missile will explode when it hits its target or at the end of its flight, the ultimate in garbage collection is performed without programmer intervention."
Sounds like HFT? But then your competitors are probably using an FPGA to respond in 300 nanoseconds, so good luck with that 5 microseconds tick-to-trade.
I don't even know how you came to the conclusion that I think that "everything has to be either manually submitted order or HFT" but that's on you.
I worked on one which was required to respond to a packet from the network within 5 microseconds of the packet arriving.
Please, don't assume all applications are mobile uis, webapps and corporate backends.