Hi, everyone, I want to implement a timeout except...

# coroutines

[Liberty Tom]

Hi, everyone, I want to implement a timeout exception retry mechanism, I wrote the blow code. But the timeout doesn’t work well, it only throw the CommConnectionException but never throw the TimeoutCancellationException. So why the timeout doesn’t work well? How to fix it?

private suspend fun realConnectBluetoothDevice(): Boolean {
        if (bluetoothCommConnection.isConnected) {
            return true
        }

        repeat(5) {
            L.e("the $it times to connect bluetooth device")
            try {
                return@realConnectBluetoothDevice blockConnect(5000L)
            } catch (e: CommConnectionException) {
                if (it == 4) {
                    throw e
                }
            } catch (e: TimeoutCancellationException) {
                if (it == 4) {
                    throw e
                }
            }
        }

        throw CommConnectionException("connect bluetooth device failed")
    }

    private suspend fun blockConnect(timeout: Long) = try {
        withTimeout(timeout) {
            withContext(Dispatchers.IO) {
                try {
                    bluetoothCommConnection.open()
                    // bluetoothCommConnection.isConnected is a Boolean value
                    bluetoothCommConnection.isConnected
                } catch (e: CommConnectionException) {
                    bluetoothCommConnection.closeImmediately()
                    throw e
                }
            }
        }
    } catch (e: TimeoutCancellationException) {
        bluetoothCommConnection.closeImmediately()
        throw e
    }

[Robert Williams]

Cancellation is cooperative - the withTimeout will cancel the block but if nothing in the block checks for the cancellation then it'll keep running as if it never happened. Most standard coroutine APIs (such as delay) will do this for you but blocking APIs have no idea that they're inside coroutines so will not

[Robert Williams]

If you know your bluetoothCommConnection supports Java interruptions you may get expected behaviour by replacing withContext with runInterruptible

[Liberty Tom]

😂Sorry, I wrote wrong code, it just like this now

[Liberty Tom]

And, bluetoothCommConnection.closeImmediately() will interrupt the bluetoothCommConnection.open() and return immediately

[Robert Williams]

If runInterruptible doesn't work but you have an interrupt method you can try calling it like:

suspendCancellableCoroutine {
                    it.invokeOnCancellation{
    interruptMethod()
                    }
                    
it.resume(blockingMethod()) { 
}
                }