speed up javac and error-prone tasks by using less resources (#11927)

* pass jvm args to javac  #11925
* Update net.ltgt.errorprone to the latest version so that jvm args are not overwritten, add -XX:+PrintFlagsFinal for debugging
* speed up the pure javac case too

It does not help to fork additional VMs (although error-prone will do
this since it messes with bootstrap classpath), so we avoid forking.

Instead it is best to tune org.gradle.jvmargs.

* use the flags consistently everywhere (tests and doc)

Co-authored-by: Robert Muir <rmuir@apache.org>

build.gradle

@@ -24,7 +24,7 @@ plugins {
   id "org.owasp.dependencycheck" version "7.2.0"
   id 'de.thetaphi.forbiddenapis' version '3.4' apply false
   id "de.undercouch.download" version "5.2.0" apply false
-  id "net.ltgt.errorprone" version "2.0.2" apply false
+  id "net.ltgt.errorprone" version "3.0.1" apply false
   id 'com.diffplug.spotless' version "6.5.2" apply false
   id 'org.barfuin.gradle.jacocolog' version "3.0.0-RC2" apply false
 }

gradle/generation/local-settings.gradle

@@ -68,7 +68,7 @@ systemProp.file.encoding=UTF-8
 # The heap seems huge but gradle runs out of memory on lower values (don't know why).
 #
 # We also open up internal compiler modules for spotless/ google java format.
-org.gradle.jvmargs=-Xmx3g \\
+org.gradle.jvmargs=-Xmx3g -XX:TieredStopAtLevel=1 -XX:+UseParallelGC -XX:ActiveProcessorCount=1 \\
  --add-exports jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED \\
  --add-exports jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED \\
  --add-exports jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED \\

gradle/hacks/turbocharge-jvm-opts.gradle

@@ -19,7 +19,8 @@
 allprojects {
     def vmOpts = [
         '-XX:+UseParallelGC',
-        '-XX:TieredStopAtLevel=1'
+        '-XX:TieredStopAtLevel=1',
+        '-XX:ActiveProcessorCount=1'
     ]
 
     // Inject vm options into custom javadoc rendering. We can't refer
@@ -38,4 +39,11 @@ allprojects {
 
         jvmArgs += vmOpts
     }
+
+    // Tweak javac to not be too resource-hungry.
+    // This applies to any JVM when javac runs forked (e.g. error-prone)
+    // Avoiding the fork entirely is best.
+    tasks.withType(JavaCompile) { JavaCompile task ->
+        task.options.forkOptions.jvmArgs += vmOpts
+    }
 }

gradle/testing/defaults-tests.gradle

@@ -47,7 +47,7 @@ allprojects {
            description: "Number of forked test JVMs"],
           [propName: 'tests.haltonfailure', value: true, description: "Halt processing on test failure."],
           [propName: 'tests.jvmargs',
-           value: { -> propertyOrEnvOrDefault("tests.jvmargs", "TEST_JVM_ARGS", "-XX:TieredStopAtLevel=1") },
+           value: { -> propertyOrEnvOrDefault("tests.jvmargs", "TEST_JVM_ARGS", "-XX:TieredStopAtLevel=1 -XX:+UseParallelGC -XX:ActiveProcessorCount=1") },
            description: "Arguments passed to each forked JVM."],
           // Other settings.
           [propName: 'tests.neverUpToDate', value: true,

help/localSettings.txt

@@ -47,7 +47,7 @@ separately from the gradle workers, for example:
 tests.jvms=3
 tests.heapsize=512m
 tests.minheapsize=512m
-tests.jvmargs=-XX:+UseParallelGC -XX:TieredStopAtLevel=1
+tests.jvmargs=-XX:+UseParallelGC -XX:TieredStopAtLevel=1 -XX:ActiveProcessorCount=1
 
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