private static Page getAtMostOnePage(Operator operator, Page sourcePage) {
// add our input page if needed
if (operator.needsInput()) {
operator.addInput(sourcePage);
}
// try to get the output page
Page result = operator.getOutput();
// tell operator to finish
operator.finish();
// try to get output until the operator is finished
while (!operator.isFinished()) {
// operator should never block
assertTrue(operator.isBlocked().isDone());
Page output = operator.getOutput();
if (output != null) {
assertNull(result);
result = output;
}
}
return result;
}
public ListenableFuture<?> process() {
checkLockNotHeld("Can not process while holding the driver lock");
try (DriverLockResult lockResult =
tryLockAndProcessPendingStateChanges(100, TimeUnit.MILLISECONDS)) {
try {
if (!lockResult.wasAcquired()) {
// this is unlikely to happen unless the driver is being
// destroyed and in that case the caller should notice notice
// this state change by calling isFinished
return NOT_BLOCKED;
}
driverContext.start();
if (!newSources.isEmpty()) {
processNewSources();
}
for (int i = 0; i < operators.size() - 1 && !driverContext.isDone(); i++) {
// check if current operator is blocked
Operator current = operators.get(i);
ListenableFuture<?> blocked = current.isBlocked();
if (!blocked.isDone()) {
current.getOperatorContext().recordBlocked(blocked);
return blocked;
}
// check if next operator is blocked
Operator next = operators.get(i + 1);
blocked = next.isBlocked();
if (!blocked.isDone()) {
next.getOperatorContext().recordBlocked(blocked);
return blocked;
}
// if current operator is finished...
if (current.isFinished()) {
// let next operator know there will be no more data
next.getOperatorContext().startIntervalTimer();
next.finish();
next.getOperatorContext().recordFinish();
} else {
// if next operator needs input...
if (next.needsInput()) {
// get an output page from current operator
current.getOperatorContext().startIntervalTimer();
Page page = current.getOutput();
current.getOperatorContext().recordGetOutput(page);
// if we got an output page, add it to the next operator
if (page != null) {
next.getOperatorContext().startIntervalTimer();
next.addInput(page);
next.getOperatorContext().recordAddInput(page);
}
}
}
}
return NOT_BLOCKED;
} catch (Throwable t) {
driverContext.failed(t);
throw t;
}
}
}