Merge pull request #7087 from mdedetrich/increase-socket-backlog-for-server-client

Set socket backlog to default size of 50

.github/workflows/ci.yml

@@ -186,6 +186,7 @@ jobs:
       shell: bash
       run: |
         # test building sbtn on Windows
+        sbt "commandProj/testOnly xsbt.IPCSpec"
         sbt "-Dsbt.io.virtual=false" nativeImage
         # test launcher script
         echo build using JDK 8, test using JDK 8, on Windows

main-command/src/main/scala/xsbt/IPC.scala

@@ -18,6 +18,7 @@ object IPC {
   private val portMin = 1025
   private val portMax = 65536
   private val loopback = InetAddress.getByName(null)
+  private[xsbt] val socketBacklog = 50 // 50 is the default backlog size for the java.net.Socket
 
   def client[T](port: Int)(f: IPC => T): T = ipc(new Socket(loopback, port))(f)
 
@@ -35,7 +36,7 @@ object IPC {
 
     def createServer(attempts: Int): ServerSocket =
       if (attempts > 0) {
-        try new ServerSocket(nextPort, 1, loopback)
+        try new ServerSocket(nextPort, socketBacklog, loopback)
         catch { case NonFatal(_) => createServer(attempts - 1) }
       } else sys.error("Could not connect to socket: maximum attempts exceeded")
 

main-command/src/test/scala/xsbt/IPCSpec.scala

@@ -0,0 +1,23 @@
+/*
+ * sbt
+ * Copyright 2011 - 2018, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ * Licensed under Apache License 2.0 (see LICENSE)
+ */
+
+package xsbt
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers._
+
+class IPCSpec extends AnyFlatSpec {
+  "server" should "allow same number of connections as determined in socket backlog" in {
+    noException should be thrownBy {
+      val server = IPC.unmanagedServer
+      (1 until IPC.socketBacklog + 1).foreach { _ =>
+        IPC.client(server.port)(identity)
+      }
+      server.close()
+    }
+  }
+}