Say there is 1 request dispatcher and multiple request consumers. If they share the same thread pool, then the request dispatcher may starve because request consumers may be hogging too much of the threads. If the request dispatcher starves, requests will be flowing into the system at a lower rate. And then your request consumers …
Instead it’s based on position. To be specific, the first column in the select sql will be mapped to the first property of the case class. Here is an example: Let’s say in the db there is a table called foo_bar foo bar fff bbb This is not desirable. But the author of Doobie won’t …
Note: Doobie’s row->case class mapping is not based on case class property name Read More »
It’s said IO.pure() means eager evaluation. But it doesn’t seem to so in this example: Here println(“print in pure”) is executed just like as if it’s IO.apply() Another example, however, discloses the truth Here is it how it works: When printTwice() is called, every expression inside it is evaluated IO.apply(println(“print in lazy”)) is evaluated as …
In Cats-effect, when is xxx inside IO.pure(xxx) executed? Read More »
Exceptions thrown in a task submitted to a thread pool will just disappear. You won’t even see the log. You can catch java.lang.Exception and handle it. But to make things even better, please catch java.lang.Throwable instead. In theory, it’s not recommended to catch a Throwable. But to be pragmatic, it’s important for you to see …
Please catch Throwable in a task submitted to a thread pool Read More »
There are a few strange things about Condition related code in Java concurrency. I’ll use the following code to show you. The code is about one cup and two threads. One thread is trying to fill it, the other to drink from it. The code uses explicit Lock + Condition API. But what I’m going …
Condition variable related code is hard to understand. So let me explain Read More »
What does the primitive do? Increase an integer value by 1 Return the original value It’s a hardware primitive, hence atomic. It can be used to implement a ticket lock. How it works Say t0, t1, t2 both arrives at line 12 Since FetchAndAdd() is atomic, the changes made by threads are serialized. Let’s assume …
First of all, it’s not the same as “compare-and-swap”. Sounds similar, but different. What it does is, Set a variable to a new value Return the old value of the variable It’s a hardware primitive, i.e. atomic. On x86 the instruction is `xchg` (There is actually no “test” , is there? ) What can it …
Lock stripping: Use different locks for different purposes on the whole data structure. For example, a read lock + a write lock Lock splitting: Use multiple locks for different parts of a data structure. For example, 16 locks are used for a ConcurrentHashMap, each guards N/16 buckets (N = total number of buckets)
If an exception is thrown from some thread and it’s not caught, it will be printed in the console. In your server, if the console output doesn’t go to any file or any log cloud, it will just disappear and you won’t understand what error has happened. Example 1: your multi-thread batch job seems to …
Make sure Java App’s console is collected somewhere Read More »
When I was learning about workflow engine, I couldn’t find a document or book that tells about it in a systematic way. So I wrote one myself after diving into it. Hope this can help first learners.