SendPort
- Dart course
- Advanced
- Lesson 3/83
- 5 min
Learn communication with SendPort and ReceivePort.
SendPort and ReceivePort
ReceivePort is the channel opened to receive messages. SendPort is the endpoint used to send messages into it. It is obtained via receivePort.sendPort.
Typical flow: the main isolate opens a ReceivePort, passes its sendPort to spawn. The new isolate, when done, replies with sendPort.send(result).
ReceivePort is a Stream; you wait for messages with await for or .first. When done, close it with close().
Two-way communication
For two-way communication between two isolates, each side opens a ReceivePort and sends its sendPort to the other. Each side can then send messages to the other.
Messages are processed in order; a single port receives one message at a time. No extra synchronization is needed.
Large objects are copied; for very large data, TransferableTypedData gives zero-copy transfer.
Practice Wait for a message with ReceivePort
Make main async. Open a port with var port = ReceivePort();. Send a message to it with port.sendPort.send('merhaba isolate'). Wait for the first message with var msg = await port.first; and print it with print(msg);.
Starter code
void main() {
// make async; open ReceivePort; sendPort.send a message; await first message
}Sample solution
import 'dart:isolate';
void main() async {
var port = ReceivePort();
port.sendPort.send('merhaba isolate');
var msg = await port.first;
print(msg);
}Expected output
merhaba isolate
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the port concepts
| Term | Meaning |
|---|---|
ReceivePort |
Message receiving channel |
SendPort |
Message sending endpoint |
.sendPort |
SendPort accessor |
.first |
First message |
2 Which interface does ReceivePort implement?
- Future
- Iterable
- Stream Correct answer
- Isolate
Explanation: ReceivePort is a Stream, yielding messages as a flow.
3 Sending a message
sendPort.____('merhaba');sendPort.send('merhaba');Explanation: SendPort.send sends a message.