refactor: use LinkedList in WaitSource.

This commit is prepare for multi-condition wait.

server/src/main/java/com/github/dtprj/dongting/fiber/Dispatcher.java

@@ -33,6 +33,7 @@
 import java.lang.invoke.MethodHandles;
 import java.lang.invoke.VarHandle;
 import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.PriorityQueue;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeUnit;
@@ -224,7 +225,8 @@ private void processScheduleFibers() {
                 continue;
             }
             if (f.source != null) {
-                f.source.removeWaiter(f);
+                // assert waiters must not null, because source is not null
+                f.source.waiters.remove(f);
                 f.source.prepare(f, true);
             }
             f.cleanSchedule();
@@ -424,13 +426,20 @@ static FrameCallResult awaitOn(WaitSource c, long millis, FrameCall resumePoint)
     static FrameCallResult awaitOn(Fiber fiber, WaitSource c, long millis, FrameCall resumePoint) {
         checkInterrupt(fiber);
         checkReentry(fiber);
+        return awaitOn0(fiber, c, millis, resumePoint);
+    }
+
+    private static FrameCallResult awaitOn0(Fiber fiber, WaitSource c, long millis, FrameCall resumePoint) {
         FiberFrame currentFrame = fiber.stackTop;
         currentFrame.resumePoint = resumePoint;
         fiber.source = c;
         fiber.scheduleTimeoutMillis = millis;
         fiber.ready = false;
         fiber.fiberGroup.dispatcher.addToScheduleQueue(millis, fiber);
-        c.addWaiter(fiber);
+        if (c.waiters == null) {
+            c.waiters = new LinkedList<>();
+        }
+        c.waiters.addLast(fiber);
         return FrameCallResult.SUSPEND;
     }
 
@@ -455,15 +464,9 @@ static void sleepUntilShouldStop(long millis, FrameCall<Void> resumePoint) {
             FiberFrame currentFrame = fiber.stackTop;
             currentFrame.resumePoint = resumePoint;
             fiber.ready = false;
-            return;
+        } else {
+            awaitOn0(fiber, g.shouldStopCondition, millis, resumePoint);
         }
-        FiberFrame currentFrame = fiber.stackTop;
-        currentFrame.resumePoint = resumePoint;
-        fiber.scheduleTimeoutMillis = millis;
-        fiber.source = g.shouldStopCondition;
-        g.shouldStopCondition.addWaiter(fiber);
-        fiber.ready = false;
-        fiber.fiberGroup.dispatcher.addToScheduleQueue(millis, fiber);
     }
 
     static void yield(FrameCall<Void> resumePoint) {
@@ -534,7 +537,8 @@ void interrupt(Fiber fiber) {
             String str;
             if (fiber.source != null) {
                 WaitSource s = fiber.source;
-                s.removeWaiter(fiber);
+                // assert waiters is not null
+                s.waiters.remove(fiber);
                 fiber.source = null;
                 str = s.toString();
             } else {

server/src/main/java/com/github/dtprj/dongting/fiber/Fiber.java

@@ -29,9 +29,6 @@ public class Fiber extends WaitSource {
     long scheduleTimeoutMillis;
     long scheduleNanoTime;
 
-    Fiber previousWaiter;
-    Fiber nextWaiter;
-
     boolean started;
     boolean ready;
     boolean finished;

server/src/main/java/com/github/dtprj/dongting/fiber/FiberCondition.java

@@ -54,7 +54,8 @@ public void signal(Fiber targetFiber) {
         if (targetFiber.source != this) {
             return;
         }
-        removeWaiter(targetFiber);
+        // assert waiters not null
+        waiters.remove(targetFiber);
         signalFiber(targetFiber, true);
     }
 

server/src/main/java/com/github/dtprj/dongting/fiber/FiberLock.java

@@ -103,9 +103,7 @@ public void unlock() {
             heldCount--;
             if (heldCount <= 0) {
                 owner = null;
-                if (firstWaiter != null) {
-                    signal0(true);
-                } else if (readLock.firstWaiter != null) {
+                if (!signal0(true)) {
                     readLock.signalAll0(true);
                 }
             }

server/src/main/java/com/github/dtprj/dongting/fiber/FiberReadLock.java

@@ -85,9 +85,7 @@ public void unlock() {
         // check fiber held this read lock?
         heldCount--;
         if (heldCount <= 0) {
-            if (writeLock.firstWaiter != null) {
-                writeLock.signal0(true);
-            }
+            writeLock.signal0(true);
         }
     }
 }

server/src/main/java/com/github/dtprj/dongting/fiber/WaitSource.java

@@ -15,13 +15,14 @@
  */
 package com.github.dtprj.dongting.fiber;
 
+import java.util.LinkedList;
+
 /**
  * @author huangli
  */
 abstract class WaitSource {
     protected final String name;
-    private Fiber lastWaiter;
-    Fiber firstWaiter;
+    LinkedList<Fiber> waiters;
     protected final FiberGroup fiberGroup;
 
     public WaitSource(String name, FiberGroup group) {
@@ -31,74 +32,16 @@ public WaitSource(String name, FiberGroup group) {
 
     protected abstract void prepare(Fiber waitFiber, boolean timeout);
 
-
-    void addWaiter(Fiber f) {
-        if (firstWaiter == null) {
-            firstWaiter = f;
-        } else {
-            lastWaiter.nextWaiter = f;
-            f.previousWaiter = lastWaiter;
-        }
-        lastWaiter = f;
-    }
-
-    void removeWaiter(Fiber f) {
-        if (f == firstWaiter) {
-            if (f == lastWaiter) {
-                firstWaiter = null;
-                lastWaiter = null;
-            } else {
-                firstWaiter = f.nextWaiter;
-                firstWaiter.previousWaiter = null;
-            }
-        } else if (f == lastWaiter) {
-            lastWaiter = f.previousWaiter;
-            lastWaiter.nextWaiter = null;
-        } else {
-            f.previousWaiter.nextWaiter = f.nextWaiter;
-            f.nextWaiter.previousWaiter = f.previousWaiter;
-        }
-        f.nextWaiter = null;
-        f.previousWaiter = null;
-    }
-
-    Fiber popTailWaiter() {
-        Fiber result = lastWaiter;
-        if (result != null) {
-            if (result == firstWaiter) {
-                firstWaiter = null;
-                lastWaiter = null;
-            } else {
-                lastWaiter = result.previousWaiter;
-                lastWaiter.nextWaiter = null;
-                result.previousWaiter = null;
-            }
-        }
-        return result;
-    }
-
-    Fiber popHeadWaiter() {
-        Fiber result = firstWaiter;
-        if (result != null) {
-            if (result == lastWaiter) {
-                firstWaiter = null;
-                lastWaiter = null;
-            } else {
-                firstWaiter = result.nextWaiter;
-                firstWaiter.previousWaiter = null;
-                result.nextWaiter = null;
-            }
-        }
-        return result;
-    }
-
-    void signal0(boolean addFirst) {
+    boolean signal0(boolean addFirst) {
         if (fiberGroup.finished) {
-            return;
+            return false;
         }
-        Fiber f = popHeadWaiter();
-        if (f != null) {
+        Fiber f;
+        if (waiters != null && (f = waiters.pollFirst()) != null) {
             signalFiber(f, addFirst);
+            return true;
+        } else {
+            return false;
         }
     }
 
@@ -115,13 +58,17 @@ void signalAll0(boolean addFirst) {
         if (fiberGroup.finished) {
             return;
         }
+        LinkedList<Fiber> waiters = this.waiters;
+        if (waiters == null) {
+            return;
+        }
         Fiber f;
         if (addFirst) {
-            while ((f = popTailWaiter()) != null) {
+            while ((f = waiters.pollLast()) != null) {
                 signalFiber(f, true);
             }
         } else {
-            while ((f = popHeadWaiter()) != null) {
+            while ((f = waiters.pollFirst()) != null) {
                 signalFiber(f, false);
             }
         }