8354460: Streaming output for attach API should be turned on by default

Reviewed-by: sspitsyn, kevinw

Author: Alex Menkov

src/hotspot/share/services/attachListener.cpp

@@ -172,8 +172,8 @@ volatile AttachListenerState AttachListener::_state = AL_NOT_INITIALIZED;
 
 AttachAPIVersion AttachListener::_supported_version = ATTACH_API_V1;
 
-// Default is false (if jdk.attach.vm.streaming property is not set).
-bool AttachListener::_default_streaming_output = false;
+// Default is true (if jdk.attach.vm.streaming property is not set).
+bool AttachListener::_default_streaming_output = true;
 
 static bool get_bool_sys_prop(const char* name, bool default_value, TRAPS) {
   ResourceMark rm(THREAD);

src/jdk.attach/share/classes/sun/tools/attach/HotSpotVirtualMachine.java

@@ -63,9 +63,8 @@ private static long pid() {
     static {
         String s = VM.getSavedProperty("jdk.attach.allowAttachSelf");
         ALLOW_ATTACH_SELF = "".equals(s) || Boolean.parseBoolean(s);
-        // For now the default is false.
         String s2 = VM.getSavedProperty("jdk.attach.allowStreamingOutput");
-        ALLOW_STREAMING_OUTPUT = "".equals(s2) || Boolean.parseBoolean(s2);
+        ALLOW_STREAMING_OUTPUT = !("false".equals(s2));
     }
 
     private final boolean selfAttach;