[server] Allow httpd to handle more than two concurrent connections

Had I read the javadocs properly I would have noticed that the thread
pool only starts growing to its maximum size if the queue is full, not
the other way round. So now we use a modified thread pool borrowed
from SO that does exactly that.

1 files changed, 60 insertions, 0 deletions

diff --git a/dozentenmodulserver/src/main/java/org/openslx/bwlp/sat/util/GrowingThreadPoolExecutor.java b/dozentenmodulserver/src/main/java/org/openslx/bwlp/sat/util/GrowingThreadPoolExecutor.java
new file mode 100644
index 00000000..becccf2f
--- /dev/null
+++ b/dozentenmodulserver/src/main/java/org/openslx/bwlp/sat/util/GrowingThreadPoolExecutor.java
@@ -0,0 +1,60 @@
+package org.openslx.bwlp.sat.util;
+
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Grows to maximum pool size before queueing. See
+ * http://stackoverflow.com/a/20153234/2043481
+ */
+public class GrowingThreadPoolExecutor extends ThreadPoolExecutor {
+	private int userSpecifiedCorePoolSize;
+	private int taskCount;
+
+	public GrowingThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime,
+			TimeUnit unit, BlockingQueue<Runnable> workQueue) {
+		super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
+		userSpecifiedCorePoolSize = corePoolSize;
+	}
+
+	@Override
+	public void execute(Runnable runnable) {
+		synchronized (this) {
+			taskCount++;
+			setCorePoolSizeToTaskCountWithinBounds();
+		}
+		super.execute(runnable);
+	}
+
+	@Override
+	protected void afterExecute(Runnable runnable, Throwable throwable) {
+		super.afterExecute(runnable, throwable);
+		synchronized (this) {
+			taskCount--;
+			setCorePoolSizeToTaskCountWithinBounds();
+		}
+	}
+
+	private void setCorePoolSizeToTaskCountWithinBounds() {
+		int threads = taskCount;
+		if (threads < userSpecifiedCorePoolSize)
+			threads = userSpecifiedCorePoolSize;
+		if (threads > getMaximumPoolSize())
+			threads = getMaximumPoolSize();
+		super.setCorePoolSize(threads);
+	}
+	
+	public void setCorePoolSize(int corePoolSize) {
+		synchronized (this) {
+			userSpecifiedCorePoolSize = corePoolSize;
+		}
+	}
+	
+	@Override
+	public int getCorePoolSize() {
+		synchronized (this) {
+			return userSpecifiedCorePoolSize;
+		}
+	}
+}
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