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Split ComputerThread/ComputerExecutor up a little

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This is an attempt to enforce better separation between ComputerThread
and ComputerExecutor. Both of these classes are pretty complex in their
own right, and the way the two bleed into each other makes it all the
more confusing!

This effectively splits the ComputerExecutor into two separate classes:
 - ComputerScheduler.Executor (with the actual implementation inside
   ComputerThread): This holds all the ComputerThread-related logic
   which used to be in ComputerExecutor, including:

    - before/after work hooks
    - is-on-thread tracking
    - virtual runtime computation

 - ComputerScheduler.Worker: This encapsulates all the computer-related
   behaviour. The actual implementation remains in ComputerExecutor.

The boundaries are still a little fuzzy here, and it's all definitely
more coupled then I'd like, but still an improvement!

There are several additional changes at the same time:

 - TimeoutState has also been split up, to better define the boundary
   between consumers (such as ComputerExecutor and ILuaMachine) and
   controllers (ComputerThread).

   The getters still live in TimeoutState, but the core logic lives in
   ManagedTimeoutState.

 - We no longer track cumulative time in the TimeoutState. Instead, we
   allow varying the timeout of a computer. When a computer is paused,
   we store the remaining time, and restore it when resuming again.

   This also allows us give a longer timeout for computer
   startup/shutdown, hopefully avoiding some of those class-not-found
   issues we've seen.

 - We try to make the state machine of how ComputerExecutors live on the
   queue a little more explicit. This is very messy/confusing -
   something I want to property test in the future.

I'm sure there's more to be done here, especially in ComputerExecutor,
but hopefully this makes future changes a little less intimidating.
This commit is contained in:
Jonathan Coates
2023-10-19 22:48:46 +01:00
parent 2228733abc
commit 0929ab577d
11 changed files with 850 additions and 560 deletions
Download Patch File Download Diff File Expand all files Collapse all files

103
projects/web/src/main/java/dan200/computercraft/core/computer/computerthread/TComputerThread.java
View File

@@ -5,57 +5,110 @@
package dan200.computercraft.core.computer.computerthread;
import cc.tweaked.web.js.Callbacks;
import dan200.computercraft.core.computer.TimeoutState;
import dan200.computercraft.core.metrics.MetricsObserver;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.teavm.jso.browser.TimerHandler;
import java.util.ArrayDeque;
import java.util.concurrent.TimeUnit;
/**
* A reimplementation of {@link ComputerThread} which, well, avoids any threading!
* An implementation of {@link ComputerScheduler} which executes work as soon as possible via
* {@link Callbacks#setImmediate(TimerHandler)}.
* <p>
* This instead just exucutes work as soon as possible via {@link Callbacks#setImmediate(TimerHandler)}. Timeouts are
* instead handled via polling, see {@link cc.tweaked.web.builder.PatchCobalt}.
* Timeouts are instead handled via polling, see {@link cc.tweaked.web.builder.PatchCobalt}.
*
* @see ComputerThread
*/
public class TComputerThread {
private static final ArrayDeque<ComputerExecutor> executors = new ArrayDeque<>();
private final TimerHandler callback = this::workOnce;
public class TComputerThread implements ComputerScheduler {
private static final Logger LOG = LoggerFactory.getLogger(TComputerThread.class);
private static final long SCALED_PERIOD = 50 * 1_000_000L;
private static final ArrayDeque<ExecutorImpl> executors = new ArrayDeque<>();
private static final TimerHandler callback = TComputerThread::workOnce;
public TComputerThread(int threads) {
}
public void queue(ComputerExecutor executor) {
if (executor.onComputerQueue) throw new IllegalStateException("Cannot queue already queued executor");
executor.onComputerQueue = true;
if (executors.isEmpty()) Callbacks.setImmediate(callback);
executors.add(executor);
@Override
public Executor createExecutor(Worker worker, MetricsObserver metrics) {
return new ExecutorImpl(worker);
}
private void workOnce() {
private static void workOnce() {
var executor = executors.poll();
if (executor == null) throw new IllegalStateException("Working, but executor is null");
if (!executor.onComputerQueue) throw new IllegalArgumentException("Working but not on queue");
executor.beforeWork();
try {
executor.work();
executor.worker.work();
} catch (Exception e) {
e.printStackTrace();
LOG.error("Error running computer", e);
executor.worker.abortWithError();
}
executor.afterWork();
if (executor.afterWork()) executors.push(executor);
if (!executors.isEmpty()) Callbacks.setImmediate(callback);
}
public boolean hasPendingWork() {
return true;
}
public long scaledPeriod() {
return 50 * 1_000_000L;
}
@Override
public boolean stop(long timeout, TimeUnit unit) {
return true;
}
/**
* The {@link Executor} for our scheduler.
*/
private static final class ExecutorImpl implements ComputerScheduler.Executor {
final ComputerScheduler.Worker worker;
private final TimeoutImpl timeout = new TimeoutImpl();
private boolean onQueue;
private ExecutorImpl(Worker worker) {
this.worker = worker;
}
@Override
public void submit() {
if (onQueue) return;
onQueue = true;
if (executors.isEmpty()) Callbacks.setImmediate(callback);
executors.add(this);
}
void beforeWork() {
if (!onQueue) throw new IllegalArgumentException("Working but not on queue");
onQueue = false;
timeout.startTimer(SCALED_PERIOD);
}
void afterWork() {
timeout.reset();
}
@Override
public TimeoutState timeoutState() {
return timeout;
}
@Override
public long getRemainingTime() {
return timeout.getRemainingTime();
}
@Override
public void setRemainingTime(long time) {
timeout.setRemainingTime(time);
}
}
private static final class TimeoutImpl extends ManagedTimeoutState {
@Override
protected boolean shouldPause() {
return true;
}
}
}