From 1c21f13b990c652acd17abefee69e26ec13d1511 Mon Sep 17 00:00:00 2001
From: Ethan Atkins <contact@ethanatkins.com>
Date: Sun, 23 Aug 2020 16:58:05 -0700
Subject: [PATCH] Reduce sbt memory utilization

The sbt Server is initialized with a callback onIncomingSocket. That
callback was created in CommandExchange and held references to a build
structure and a state. Neither the state nor structure would ever go out
of scope so they effectively leaked. It is possible for each
NetworkChannel to access a recent instance of state through the
CommandExchange.withState method. Using this, we can eliminate the
references to state and build structure in the onIncomingSocket
callback. In the sbt project, this reduced the memory utilization by
about 50mb on startup.
---
 .../scala/sbt/internal/CommandExchange.scala  |  3 ---
 .../sbt/internal/server/NetworkChannel.scala  | 21 ++++++++++---------
 2 files changed, 11 insertions(+), 13 deletions(-)

diff --git a/main/src/main/scala/sbt/internal/CommandExchange.scala b/main/src/main/scala/sbt/internal/CommandExchange.scala
index 7b3b48901..58ec187fd 100644
--- a/main/src/main/scala/sbt/internal/CommandExchange.scala
+++ b/main/src/main/scala/sbt/internal/CommandExchange.scala
@@ -195,13 +195,10 @@ private[sbt] final class CommandExchange {
         new NetworkChannel(
           name,
           socket,
-          Project structure s,
           auth,
           instance,
           handlers,
-          s.log,
           mkAskUser(name),
-          Option(lastState.get),
         )
       subscribe(channel)
     }
diff --git a/main/src/main/scala/sbt/internal/server/NetworkChannel.scala b/main/src/main/scala/sbt/internal/server/NetworkChannel.scala
index 1c7d93484..7bf6d2727 100644
--- a/main/src/main/scala/sbt/internal/server/NetworkChannel.scala
+++ b/main/src/main/scala/sbt/internal/server/NetworkChannel.scala
@@ -54,13 +54,10 @@ import sbt.internal.util.ProgressState
 final class NetworkChannel(
     val name: String,
     connection: Socket,
-    protected val structure: BuildStructure,
     auth: Set[ServerAuthentication],
     instance: ServerInstance,
     handlers: Seq[ServerHandler],
-    val log: Logger,
     mkUIThreadImpl: (State, CommandChannel) => UITask,
-    state: Option[State],
 ) extends CommandChannel { self =>
   def this(
       name: String,
@@ -74,15 +71,14 @@ final class NetworkChannel(
     this(
       name,
       connection,
-      structure,
       auth,
       instance,
       handlers,
-      log,
       new UITask.AskUserTask(_, _),
-      None
     )
 
+  def log: Logger = StandardMain.exchange.withState(_.log)
+
   private val running = new AtomicBoolean(true)
   private val delimiter: Byte = '\n'.toByte
   private val out = connection.getOutputStream
@@ -411,9 +407,12 @@ final class NetworkChannel(
   protected def onSettingQuery(execId: Option[String], req: SettingQuery) = {
     if (initialized) {
       import sbt.protocol.codec.JsonProtocol._
-      SettingQuery.handleSettingQueryEither(req, structure) match {
-        case Right(x) => respondResult(x, execId)
-        case Left(s)  => respondError(ErrorCodes.InvalidParams, s, execId)
+      StandardMain.exchange.withState { s =>
+        val structure = Project.extract(s).structure
+        SettingQuery.handleSettingQueryEither(req, structure) match {
+          case Right(x) => respondResult(x, execId)
+          case Left(s)  => respondError(ErrorCodes.InvalidParams, s, execId)
+        }
       }
     } else {
       log.warn(s"ignoring query $req before initialization")
@@ -792,7 +791,9 @@ final class NetworkChannel(
     private[this] val blockedThreads = ConcurrentHashMap.newKeySet[Thread]
     override private[sbt] val progressState: ProgressState = new ProgressState(
       1,
-      state.flatMap(_.get(Keys.superShellMaxTasks.key)).getOrElse(SysProp.supershellMaxTasks)
+      StandardMain.exchange
+        .withState(_.get(Keys.superShellMaxTasks.key))
+        .getOrElse(SysProp.supershellMaxTasks)
     )
     override def getWidth: Int = getProperty(_.width, 0).getOrElse(0)
     override def getHeight: Int = getProperty(_.height, 0).getOrElse(0)