Manage the thread-local IO buffer manually rather than using a finalizer

* Avoids creating the finalizer thread very early when not really needed.
* Fixes sharing being triggered by operations using the thread IO buffer
  such as File.read.

Author: eregon

spec/truffle/thread_safe_objects_spec.rb

@@ -281,4 +281,8 @@ def wb; @wb; end
     ruby_exe("p Truffle::Debug.shared?(Object)").should == "false\n"
   end
 
+  it "thread-local IO buffers which should not trigger sharing" do
+    ruby_exe("File.read(#{__FILE__.inspect}); p Truffle::Debug.shared?(Object)").should == "false\n"
+  end
+
 end

src/main/java/org/truffleruby/core/support/IONodes.java

@@ -477,8 +477,6 @@ public int write(int fd, DynamicObject string) {
     @Primitive(name = "io_get_thread_buffer", needsSelf = false)
     public static abstract class GetThreadBufferNode extends PrimitiveArrayArgumentsNode {
 
-        private static final ThreadLocal<Pointer> THREAD_BUFFER_THREAD_LOCAL = ThreadLocal.withInitial(() -> Pointer.NULL);
-
         @Specialization
         public DynamicObject getThreadBuffer(long size,
                 @Cached("create()") AllocateObjectNode allocateObjectNode) {
@@ -487,13 +485,15 @@ public DynamicObject getThreadBuffer(long size,
 
         @TruffleBoundary
         public static Pointer getBuffer(RubyContext context, long size) {
-            final Pointer buffer = THREAD_BUFFER_THREAD_LOCAL.get();
+            final DynamicObject rubyThread = context.getThreadManager().getCurrentThread();
+            final Pointer buffer = Layouts.THREAD.getIoBuffer(rubyThread);
+
             if (buffer.getSize() >= size) {
                 return buffer;
             } else {
+                buffer.freeNoAutorelease();
                 final Pointer newBuffer = Pointer.malloc(Math.max(size * 2, 1024));
-                newBuffer.enableAutorelease(context.getFinalizationService());
-                THREAD_BUFFER_THREAD_LOCAL.set(newBuffer);
+                Layouts.THREAD.setIoBuffer(rubyThread, newBuffer);
                 return newBuffer;
             }
         }

src/main/java/org/truffleruby/core/thread/ThreadLayout.java

@@ -18,6 +18,7 @@
 import org.truffleruby.core.InterruptMode;
 import org.truffleruby.core.basicobject.BasicObjectLayout;
 import org.truffleruby.core.fiber.FiberManager;
+import org.truffleruby.extra.ffi.Pointer;
 import org.truffleruby.language.threadlocal.ThreadLocalGlobals;
 
 import java.util.List;
@@ -45,6 +46,7 @@ Object[] build(
             @Nullable @Volatile Object value,
             AtomicBoolean wakeUp,
             @Volatile int priority,
+            Pointer ioBuffer,
             DynamicObject threadGroup,
             String sourceLocation,
             DynamicObject name);
@@ -85,6 +87,9 @@ Object[] build(
     int getPriority(DynamicObject object);
     void setPriority(DynamicObject object, int value);
 
+    Pointer getIoBuffer(DynamicObject object);
+    void setIoBuffer(DynamicObject object, Pointer value);
+
     DynamicObject getThreadGroup(DynamicObject object);
     void setThreadGroup(DynamicObject object, DynamicObject value);
 

src/main/java/org/truffleruby/core/thread/ThreadManager.java

@@ -183,6 +183,7 @@ private Object[] packThreadFields(DynamicObject currentGroup, String info) {
                 null,
                 new AtomicBoolean(false),
                 Thread.NORM_PRIORITY,
+                Pointer.NULL,
                 currentGroup,
                 info,
                 nil());
@@ -336,6 +337,8 @@ public void cleanup(DynamicObject thread, Thread javaThread) {
         final FiberManager fiberManager = Layouts.THREAD.getFiberManager(thread);
         fiberManager.shutdown(javaThread);
 
+        Layouts.THREAD.getIoBuffer(thread).freeNoAutorelease();
+
         unregisterThread(thread);
         Layouts.THREAD.setThread(thread, null);