for(int i=0;i<10000; ++i){
// do nothing just compute hash again and again.
hash = str.hashCode();
}
"do nothing" is correct, "again and again" not so much. Java caches the hash code for Strings and since the JIT knows that (at least in recent version[1]) it might even remove this loop entirely.
I'm actually pretty curious to see what this method does on versions that don't have the optimization to treat hashCodes as quasi-final.
A quick test using Java 17 shows it's not being optimized away _completely_, but it's taking...~1 ns per iteration, which is not enough to compute a hash code.
Edit: I'm being silly. It will just compute the hashcode the first time, and then repeatedly check that it's cached and return it. So the JIT doesn't have to do any _real_ work to make this skip the hash code calculation.
So most likely, the effective code is:
computeHashCode();
for (int i = 0; i < 10000; i++) {
if (false) { // pretend this wouldn't have dead code elimination, and the boolean is actually checked
computeHashCode();
}
}Btw I found most of the jmh samples interesting. IMO a quite effective mix of example and documentation. (and I'm not sure there is even much other official documentation)
[1] https://github.com/openjdk/jmh/blob/master/jmh-samples/src/m... [2] https://github.com/openjdk/jmh/blob/872b7203c294d90c17766d19...
The nasal "m" takes on the form of the nasal in the row/class of the letter that follows it. As "ñ" is the nasal of the "c" class, the "m" becomes "ñ"
Writing Sanskrit terms using the roman script without using something like IAST/ISO-15919 is a pain in the neck. They are going to be mispronounced one way or the other. I try to get the ISO-15919 form and strip away everything that is not a-z.
So, सञ्चिका (sañcikā) = sancika
You probably want to keep the "ch," as the average English speaker is not going to remember that the "c" is the "ch" of "cheese" and not "see."
All nasals becoming anusvaras is something Hindi/Marathi and other languages using the Devanagari script do. Sanskrit uses the specific form of the nasal when available.
I will try to incorporate most of your feedback. Your commments have given me much to learn.
This project was started to just learn more about multithreading in a practical way. I think I succeeded with that.
Also, modern filing systems are all thread safe. You can have multiple threads reading and even writing in parallel on different CPU cores.
No, there is no separate kernel "executing". When you do a syscall, your thread becomes kernel mode and it executes the function behind the syscall, then when it's done, your thread reverts to user mode.
A context switch is when one thread is being swapped out for another. Now the syscall could internally spawn a thread and context switch to that, but I'm not sure if this happens in read() or any syscall for that matter.
Have the OS handle memory paging and buffering for you and then use Java's parallel algorithms to do concurrent processing.
Create a "MappedByteBuffer" and mmap the file into memory.
If the file is too large, use an "AsynchronousFileChannel" and asynchronously read + process segments of the buffer.
https://gavinray97.github.io/blog/panama-not-so-foreign-memo...
Then again, if you're in Java/JVM land you're probably not building bleeding edge DBs ala ScyllaDB. But I'm somewhat surprised at the lack of projects in this space. One would think this would pair well with some of the reactive stream implementations so that you wouldn't have to reimplement things like backpressure, etc.
b) SycllaDB is not bleeding edge. It uses the relatively old now DPDK.
c) There are countless reactive stream implementations e.g. https://vertx.io/docs/vertx-reactive-streams/java/
It is not wrong, but at least put yourself into it a bit.
You didn't learn anything. You didn't accomplish anything. And no one including you respects it.
And this project is just a start.