[feature] create BEP connection on demands instead of keeping it as a…

… service (#356)

Create BEP connection on demands instead of keeping it as a service

- Background
Significantly reduces memory footprint of the application, because the
never-cleaned BepServer instance was holding a `BepOutputBuilder bepOutputBuilder`
field which in turn was holding all BEP messages that has been received since the
prevous build.

So the reason for this change is:
1. There's no point of having a socket handle and other sources laying in memory,
   in particular because it's easy to make a mistake of keeping too much data.
2. BepServer setup is cheap
3. It will be easier to provide different peb handlers for different calls.

- Memory footprint comparison
The heap size in of this app in idle, for a project containing 2000 targets, is reduced from
more than ~2GB to ~0.5GB.

Bazel BSP 2.5.1 (idle, after 2000k targets import)
```
$ jcmd 11429 GC.heap_info
11429:
 garbage-first heap   total 5382144K, used 3219933K [0x0000000673800000, 0x0000000800000000)
  region size 4096K, 40 young (163840K), 39 survivors (159744K)
 Metaspace       used 45658K, committed 46016K, reserved 1097728K
  class space    used 5045K, committed 5248K, reserved 1048576K
$ jcmd 11429 GC.run
11429:
Command executed successfully
$ jcmd 11429 GC.heap_info
11429:
 garbage-first heap   total 5382144K, used 2161982K [0x0000000673800000, 0x0000000800000000)
  region size 4096K, 0 young (0K), 0 survivors (0K)
 Metaspace       used 45658K, committed 46016K, reserved 1097728K
  class space    used 5045K, committed 5248K, reserved 1048576K

```

Bazel BSP now:
```
$ jcmd 9381 GC.heap_info
9381:
 garbage-first heap   total 4001792K, used 2190915K [0x0000000673800000, 0x0000000800000000)
  region size 4096K, 48 young (196608K), 47 survivors (192512K)
 Metaspace       used 46417K, committed 46784K, reserved 1097728K
  class space    used 5114K, committed 5312K, reserved 1048576K
$ jcmd 9381 GC.run
9381:
Command executed successfully
$ jcmd 9381 GC.heap_info
9381:
 garbage-first heap   total 1900544K, used 556282K [0x0000000673800000, 0x0000000800000000)
  region size 4096K, 0 young (0K), 0 survivors (0K)
 Metaspace       used 46417K, committed 46784K, reserved 1097728K
  class space    used 5114K, committed 5312K, reserved 1048576K

```

CHANGELOG.md

@@ -9,6 +9,8 @@
 
 - Project view file flag for disabling trace log.
   | [#344](https://github.com/JetBrains/bazel-bsp/pull/344)
+- Create BEP connection on demands instead of keeping it as a service (reduces memory footprint)
+  | [#356](https://github.com/JetBrains/bazel-bsp/pull/356)
 
 ## [2.5.1] - 08.02.2023
 

server/src/main/java/org/jetbrains/bsp/bazel/server/BazelBspServer.kt

@@ -1,17 +1,14 @@
 package org.jetbrains.bsp.bazel.server
 
 import ch.epfl.scala.bsp4j.BuildClient
-import io.grpc.ServerBuilder
 import org.eclipse.lsp4j.jsonrpc.Launcher
 import org.jetbrains.bsp.bazel.bazelrunner.BazelRunner
 import org.jetbrains.bsp.bazel.logger.BspClientLogger
 import org.jetbrains.bsp.bazel.logger.BspClientTestNotifier
-import org.jetbrains.bsp.bazel.server.bep.BepServer
 import org.jetbrains.bsp.bazel.server.bsp.*
 import org.jetbrains.bsp.bazel.server.bsp.info.BspInfo
 import org.jetbrains.bsp.bazel.server.bsp.managers.BazelBspCompilationManager
 import org.jetbrains.bsp.bazel.server.common.ServerContainer
-import org.jetbrains.bsp.bazel.server.diagnostics.DiagnosticsService
 import org.jetbrains.bsp.bazel.server.sync.BspProjectMapper
 import org.jetbrains.bsp.bazel.server.sync.ExecuteService
 import org.jetbrains.bsp.bazel.server.sync.ProjectSyncService
@@ -72,9 +69,8 @@ class BazelBspServer(
         val client = launcher.remoteProxy
         bspClientLogger.initialize(client)
         bspClientTestNotifier.initialize(client)
-        val bepServer = BepServer(client, DiagnosticsService(workspaceRoot))
-        compilationManager.setBepServer(bepServer)
-        bspIntegrationData.server = ServerBuilder.forPort(0).addService(bepServer).build()
+        compilationManager.setClient(client)
+        compilationManager.setWorkspaceRoot(workspaceRoot)
     }
 
     private fun createLauncher(bspIntegrationData: BspIntegrationData): Launcher.Builder<BuildClient> {
@@ -89,8 +85,4 @@ class BazelBspServer(
 
         return builder
     }
-
-    fun setBesBackendPort(port: Int) {
-        bazelRunner.setBesBackendPort(port)
-    }
 }

server/src/main/java/org/jetbrains/bsp/bazel/server/ServerInitializer.kt

@@ -53,10 +53,7 @@ object ServerInitializer {
             )
             val bspServer = BazelBspServer(bspInfo, workspaceContextProvider, Path(cliArgs.bazelWorkspaceRoot))
             bspServer.startServer(bspIntegrationData)
-            val server = bspIntegrationData.server.start()
-            bspServer.setBesBackendPort(server.port)
-            bspIntegrationData.launcher.startListening()
-            server.awaitTermination()
+            bspIntegrationData.launcher.startListening().get()
         } catch (e: Exception) {
             e.printStackTrace(System.err)
             hasErrors = true

server/src/main/java/org/jetbrains/bsp/bazel/server/bloop/BloopExporter.java

@@ -102,7 +102,6 @@ private void initializeClient(ServerContainer serverContainer, BloopBuildClient
     var bepServer =
         new BepServer(
             client, new DiagnosticsService(serverContainer.getBazelInfo().getWorkspaceRoot()));
-    serverContainer.getCompilationManager().setBepServer(bepServer);
 
     var grpcServer = ServerBuilder.forPort(0).addService(bepServer).build();
     try {

server/src/main/java/org/jetbrains/bsp/bazel/server/bsp/BspIntegrationData.kt

@@ -15,5 +15,4 @@ data class BspIntegrationData(
     val traceWriter: PrintWriter?,
 ) {
     lateinit var launcher: Launcher<BuildClient>
-    lateinit var server: Server
 }

server/src/main/java/org/jetbrains/bsp/bazel/server/bsp/managers/BUILD

@@ -10,6 +10,8 @@ java_library(
         "//executioncontext/workspacecontext",
         "//server/src/main/java/org/jetbrains/bsp/bazel/server/bep",
         "//server/src/main/java/org/jetbrains/bsp/bazel/server/bsp/utils",
+        "//server/src/main/java/org/jetbrains/bsp/bazel/server/diagnostics",
+        "@io_bazel//third_party/grpc:grpc-jar_checked_in",
         "@maven//:org_eclipse_lsp4j_org_eclipse_lsp4j_jsonrpc",
     ],
 )

server/src/main/java/org/jetbrains/bsp/bazel/server/bsp/managers/BazelBspCompilationManager.java

@@ -1,16 +1,23 @@
 package org.jetbrains.bsp.bazel.server.bsp.managers;
 
+import ch.epfl.scala.bsp4j.BuildClient;
+import io.grpc.ServerBuilder;
 import io.vavr.collection.List;
 import io.vavr.collection.Seq;
 import org.eclipse.lsp4j.jsonrpc.CancelChecker;
 import org.jetbrains.bsp.bazel.bazelrunner.BazelRunner;
 import org.jetbrains.bsp.bazel.server.bep.BepServer;
+import org.jetbrains.bsp.bazel.server.diagnostics.DiagnosticsService;
 import org.jetbrains.bsp.bazel.workspacecontext.TargetsSpec;
 
+import java.io.IOException;
+import java.nio.file.Path;
+
 public class BazelBspCompilationManager {
 
   private final BazelRunner bazelRunner;
-  private BepServer bepServer;
+  private BuildClient client;
+  private Path workspaceRoot;
 
   public BazelBspCompilationManager(BazelRunner bazelRunner) {
     this.bazelRunner = bazelRunner;
@@ -23,18 +30,34 @@ public BepBuildResult buildTargetsWithBep(CancelChecker cancelChecker, TargetsSp
   public BepBuildResult buildTargetsWithBep(
       CancelChecker cancelChecker,
       TargetsSpec targetSpecs, Seq<String> extraFlags, String originId) {
-    var result =
-        bazelRunner
-            .commandBuilder()
-            .build()
-            .withFlags(extraFlags.asJava())
-            .withTargets(targetSpecs)
-            .executeBazelBesCommand(originId)
-            .waitAndGetResult(cancelChecker, false);
-    return new BepBuildResult(result, bepServer.getBepOutput());
+    var bepServer = new BepServer(client, new DiagnosticsService(workspaceRoot));
+    var server = ServerBuilder.forPort(0).addService(bepServer).build();
+    try {
+      server.start();
+    } catch (IOException e) {
+      throw new RuntimeException(e);
+    }
+    bazelRunner.setBesBackendPort(server.getPort());
+    try {
+      var result =
+              bazelRunner
+                      .commandBuilder()
+                      .build()
+                      .withFlags(extraFlags.asJava())
+                      .withTargets(targetSpecs)
+                      .executeBazelBesCommand(originId)
+                      .waitAndGetResult(cancelChecker, true);
+      return new BepBuildResult(result, bepServer.getBepOutput());
+    } finally {
+        server.shutdown();
+    }
+  }
+
+  public void setClient(BuildClient client) {
+    this.client = client;
   }
 
-  public void setBepServer(BepServer bepServer) {
-    this.bepServer = bepServer;
+  public void setWorkspaceRoot(Path workspaceRoot) {
+    this.workspaceRoot = workspaceRoot;
   }
 }