Synchronized lists

Hey guys!
A bit of concurrency question here. I was using

CopyOnWriteArrayList

CopyOnWriteArrayList

to have a threadsafe list that I can write to from different threads. The whole purpose was that I need to make a multitude ap API calls, process the information and save it to a collection. The API calls could be run concurrently, so I would make the process faster, so I needed a threadsafe implementation of

List

List

. I found that

CopyOnWriteArrayList

CopyOnWriteArrayList

is such an implementation, but it wasn't working well. I know how many items I need to have in the collection after finishing, and that amount wwas always lower. I tried then using

Collections.synchronizedList()

Collections.synchronizedList()

which had a better result, but still not the amount I needed. When I did the process sequentially, then I got the exact number of items I needed. So something is wrong with synchronization, or is there something I need to know, that I am not aware of synchronized lists in Java fro them to be truly threadsafe? Coding wise I initialized the array with

Collections.synchronizedList()

Collections.synchronizedList()

, and used virtual threads for the API calls, in which the writing is done.
A sample of what I did:

...
//I have a list with data for the API calls called: issues
List<MyType> list = Collections.synchronizedList(new ArrayList);
try(var exector = Executor.newVirtualThreadPerTaskExecutor()) {
  while(issues.hasNext()){
    MyType response = makeAPICall(issues.next());
    list.add(response);
  }
}
...

...
//I have a list with data for the API calls called: issues
List<MyType> list = Collections.synchronizedList(new ArrayList);
try(var exector = Executor.newVirtualThreadPerTaskExecutor()) {
  while(issues.hasNext()){
    MyType response = makeAPICall(issues.next());
    list.add(response);
  }
}
...

Thank you for the answers in advance!

JC|HCL

Java Community | Help. Code. Learn.•6mo ago•

14 replies

Glayer

Synchronized lists

Hey guys!
A bit of concurrency question here. I was using

CopyOnWriteArrayList

CopyOnWriteArrayList

List

List

. I found that

CopyOnWriteArrayList

CopyOnWriteArrayList

is such an implementation, but it wasn't working well. I know how many items I need to have in the collection after finishing, and that amount wwas always lower. I tried then using

Collections.synchronizedList()

Collections.synchronizedList()

Collections.synchronizedList()

Collections.synchronizedList()

, and used virtual threads for the API calls, in which the writing is done.
A sample of what I did:

...
//I have a list with data for the API calls called: issues
List<MyType> list = Collections.synchronizedList(new ArrayList);
try(var exector = Executor.newVirtualThreadPerTaskExecutor()) {
  while(issues.hasNext()){
    MyType response = makeAPICall(issues.next());
    list.add(response);
  }
}
...

...
//I have a list with data for the API calls called: issues
List<MyType> list = Collections.synchronizedList(new ArrayList);
try(var exector = Executor.newVirtualThreadPerTaskExecutor()) {
  while(issues.hasNext()){
    MyType response = makeAPICall(issues.next());
    list.add(response);
  }
}
...

Thank you for the answers in advance!

Synchronized lists

Synchronized lists

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