11–20 of 33 posts
I really enjoy the completeness of this publication, additionally the ability for me to read it later from an epub is great. This reminds me when the Java Pub House did a few podcasts on Garbage Collections and performance ( http://www.javapubhouse.com/2012/04/episode-22-garbage-man-i... )
Would also love details on the author's workflow and automation behind this.
7k views, 155 upvotes, 1 comment...
I was skeptical at first as well, but your own stats show a different picture: the site gets a lot of views, which correlates with the upvotes. No comments is probably due to the fact that people use upvoting as a mechanism to save links to material (which might be of use later)
Earlier quoted context omitted.
I was skeptical at first as well, but your own stats show a different picture: the site gets a lot of views, which correlates with the upvotes. No comments is probably due to the fact that people use upvoting as a mechanism to save links to material (which might be of use later)
To clarify, I don't think this is improper use of the upvote mechanism, I was just hoping for more engagement with the comment feature of Hacker News, given the 7k click thrus.
" for (...) { synchronized (obj) { // something } }
…could it optimize into this?
synchronized (this) { for (...) { The answer would be no in general, I think, since it is unsafe.
Moving the entire loop into the synchronized block would make the statement marked XXX above, i.e. "for (...)" execute inside the synchronized block, which has the potential to change the semantics (for example, the statement may include an rpc, and we don't want to make that rpc under the lock).
The earlier optimization of
synchronized (this) { statement1; }
synchronized (this) { statement2; }
to
synchronized (this) { statement1; statement2; }
is safe.
Earlier quoted context omitted.
I was skeptical at first as well, but your own stats show a different picture: the site gets a lot of views, which correlates with the upvotes. No comments is probably due to the fact that people use upvoting as a mechanism to save links to material (which might be of use later)
To clarify, I don't think this is improper use of the upvote mechanism, I was just hoping for more engagement with the comment feature of Hacker News, given the 7k click thrus.
I don't even know what sense of the word is intended. Is it "park" like a city or amusement park that you visit, and the idea is that you enjoy a variety of different activities while you're there? Is it "park" like a ballpark, and the analogy is that sporting events take place there and each one of these topics is an event? Is it somehow "park" like a parking lot? Maybe "park" is a too-literal translation from another language where the corresponding word has a meaning that the English one doesn't?
I'm trying to guess based on context, but none of these really seems to fit.
This is of no real consequence except curiosity, but I'm at a loss to understand what "park" means in the title. I don't even know what sense of the word is intended. Is it "park" like a city or amusement park that you visit, and the idea is that you enjoy a variety of different activities while you're there? Is it "park" like a ballpark, and the analogy is that sporting events take place there and each one of these…
This is of no real consequence except curiosity, but I'm at a loss to understand what "park" means in the title. I don't even know what sense of the word is intended. Is it "park" like a city or amusement park that you visit, and the idea is that you enjoy a variety of different activities while you're there? Is it "park" like a ballpark, and the analogy is that sporting events take place there and each one of these…
Regarding the question in the 1st topic: ( https://shipilev.net/jvm-anatomy-park/1-lock-coarsening-for-... ) " for (...) { synchronized (obj) { // something } } …could it optimize into this? synchronized (this) { for (...) { The answer would be no in general, I think, since it is unsafe. Moving the entire loop into the synchronized block would make the statement marked XXX above, i.e. "for (...)" execute inside the…
That's not change in semantics. The JVM doesn't provide any guarantees about parallelism or scheduling semantics in the first place so how can you possibly argue about the semantics of holding a lock too long?
And it's unsafe? For what definition of safety?
But in practice - yes you obviously wouldn't do this if the code in the loop control code had any side effects.
Regarding the question in the 1st topic: ( https://shipilev.net/jvm-anatomy-park/1-lock-coarsening-for-... ) " for (...) { synchronized (obj) { // something } } …could it optimize into this? synchronized (this) { for (...) { The answer would be no in general, I think, since it is unsafe. Moving the entire loop into the synchronized block would make the statement marked XXX above, i.e. "for (...)" execute inside the…
I do agree that it's not a "safe" optimization in the extreme general case (so don't go rewriting your code assuming it's equivalent!), but in the case where the loop is a candidate for unrolling it works just fine. Imagine you had a more CPU- or memory-bound workload, and these benchmarks are a whole lot more interesting.
Put another way: if there's an RPC call in the for loop, the time spent in the RPC will dwarf the work involved in executing loop itself so ... odds are good it's not going to be a candidate for unrolling anyways. :)