RFR(S): 8252090: JFR: StreamWriterHost::write_unbuffered() stucks in an infinite loop OpenJDK (build 13.0.1+9)

[Markus Gronlund]

Greetings,

Please review the following changeset:

Bug: https://bugs.openjdk.java.net/browse/JDK-8252090 
Webrev: http://cr.openjdk.java.net/~mgronlun/8252090/webrev00/
Testing: jdk_jfr

Thanks to Harold Seigel for initial triage and suggestion for how to address this.

Thanks
Markus