compute function different from describe? #116697
Description
import 'dart:isolate';
import 'package:flutter/foundation.dart';
class BackgroundPlus {
final PlusData plusData;
BackgroundPlus(this.plusData);
Future<int> computeInBackground() async {
return compute(_computeEntry, plusData);
}
int _computeEntry(PlusData plusData) {
print(
"_computeEntry isolate: ${Isolate.current.debugName}@${Isolate.current.hashCode}");
return plusData.a + plusData.b;
}
}
class PlusData {
final int a;
final int b;
PlusData(this.a, this.b);
}
void main() async {
print(
"main isolate: ${Isolate.current.debugName}@${Isolate.current.hashCode}");
final data = await BackgroundPlus(PlusData(2, 3)).computeInBackground();
print("data=$data");
}
After I run code below, this message on console is:
Which means I can run compute function with memeber function and user-defined class. But the descibe of the compute function is:
callback:
/// {@template flutter.foundation.compute.callback}
/// Qualifying functions include:
///
/// * top-level functions
/// * static methods
/// * closures that only capture objects that can be sent to an isolate
message
/// There are limitations on the values that can be sent and received to and
/// from isolates. These limitations constrain the values of `Q` and `R` that
/// are possible. See the discussion at [SendPort.send].
Why this works? One possible reason I guess is that Isolate.spawn will copy all memory hold by its message param to the new isolate. After I read descibe of Isolate.spaw carefully, I didn't find any limitation on message param. So I guess the _IsolateConfiguration params passed to compute function will be copied too. Since callback is a member funtion pointer, the whole object will be deep copied too.
If my guess is correct, the describe of compute is misleading user force use limited function and message type; Or else, use member function and user defined class member will bring some harm?