"start_batch was called incorrectly" on gRPC unary call - php

Question

I make an unary call from PHP code like that:
public function getByIDs(array $ids): array
{
$request = new GetByIDsRequest();
$request->setIDs($ids);
$grpcRequest = $this->client->GetByIDs($request, [], ['timeout' => $this->waitTimeout]);
$response = $this->callWithRetries($grpcRequest);
if (!$response->isOk()) {
$status = $response->getStatus();
throw new GrpcServerException(__FUNCTION__, $status->getDetails(), (int)$status->getCode());
}
... // business logic here
}
private function callWithRetries(\Grpc\UnaryCall $grpcRequest): GrpcUnaryCallResponse
{
$response = null;
for ($attempt = 0; $attempt <= self::$maxRetries; $attempt++) {
if ($attempt > 0) {
usleep(mt_rand(1, 5) * self::$waitBeforeRetry);
}
$response = $this->unaryCall($grpcRequest);
$status = $response->getStatus()->getCode();
if ($response->isOk() || !self::isRetryable($status)) {
return $response;
}
}
return $response;
}
protected function unaryCall(UnaryCall $call): GrpcUnaryCallResponse
{
[$response, $status] = $call->wait();
return new GrpcUnaryCallResponse(
$response,
new GrpcStatus($status)
);
}
Sometimes I get the LogicException with message "start_batch was called incorrectly". Any thoughts how to deal with that exception and what is the root cause?

Answer 1

After some investigation I found out that the problem occurs because of reusing the instance of \Grpc\UnaryCall in retries. You must not do that otherwise you get a core dump.
The reason we got the LogicException but not a core dump is using a patched gRPC extension.
Some more technical details you can find in this issue