What’s the opposite of “embarrassingly parallel”?
Inherently sequential. Example: The number of women will not reduce the length of pregnancy.
concurrency
Concurrent generic data structure without deadlocks or resource starvation
You can set up a worker thread to process all requests in a deterministic way, so nobody gets starved. This strategy would be reasonably efficient and immune to livelock. — yes, this is a horrible name createManagerFactory :: a -> IO ((IO a), IO (((a -> a) -> IO a))) IO a is an action …
Difference between Java Concurrency, Akka and RxJava?
According to Mathias Doenitz at this point in time RxJava doesn’t have back pressure unlike Akkas Reactive Streams implementation. But RxJava seems to be working on adding back pressure. Both frameworks will be able to interact through the reactive streaming spi. So you will be able to do very very similar things. According to Mathias …
postgreSQL concurrently change column type from int to bigint
If you don’t have foreign keys pointing your id you could add new column, fill it, drop old one and rename new to old: alter table my_table add column new_id bigint; begin; update my_table set new_id = id where id between 0 and 100000; commit; begin; update my_table set new_id = id where id between …
Does Thread.yield() do anything if we have enough processors to service all threads?
Whenever a thread calls the Thread.yield() method, it gives a hint to the thread scheduler that it is ready to pause its execution. The thread scheduler is free to ignore this hint. If any thread executes the yield method, the thread scheduler checks if there is any runnable (waiting to be executed) thread with same …
Optimistic Locking by concrete (Java) example
Normally when you look into optimistic locking you also use a library like Hibernate or an other JPA-Implementation with @Version support. Example could read like this: public class Person { private String firstName; private String lastName; private int age; private Color favoriteColor; @Version private Long version; } while obviously there is no point of adding …
Java BlockingQueue take() vs poll()
Blocking is likely more efficient. In the background, the thread that initially calls take() goes to sleep if there is no element available, letting other threads do whatever they need to do. The methods that add elements to the Queue will then wake up waiting threads when an element is added, so minimal time is …
Transaction deadlock for select query
My init understanding is that a Select query won’t lock a table, or won’t cause a deadlock This understanding is wrong. SELECT queries take shared locks on the rows they analyze. Shared locks may conflict exclusive locks from update/delete/insert statements. Two SELECT statements are not going to deadlock, but a SELECT can deadlock with an …
Why doesn’t this thread pool get garbage collected?
This doesn’t really have anything to do with GC being non-deterministic, although it doesn’t help! (That is one cause in your example, but even if we ‘fixed’ it to eat up memory and force a collection, it still wouldn’t finalize) The Worker threads that the executor creates are inner classes that have a reference back …
Can modern x86 hardware not store a single byte to memory?
TL:DR: On every modern ISA that has byte-store instructions (including x86), they’re atomic and don’t disturb surrounding bytes. (I’m not aware of any older ISAs where byte-store instructions could “invent writes” to neighbouring bytes either.) The actual implementation mechanism (in non-x86 CPUs) is sometimes an internal RMW cycle to modify a whole word in a …