RFR: 6988: Initial implementation of JFR binary format writer [v6]

[Alexander Kuznetsov]

On Wed, 13 Jan 2021 17:44:41 GMT, Jaroslav Bachorik <jbachorik at openjdk.org> wrote:

>> The files now need 2021 added to the copyright notices.
>
> All affected files should have the copyright updated now

Hi! We at JetBrains tried to use this writer to make tests for our JMC fork support. It works fine, however, it seems that almost every type is assumed to have constant pool (`org.openjdk.jmc.flightrecorder.writer.ConstantPool#writeValueType`). But that’s not always true; for example, async-profiler and JFR write `jdk.types.StackFrame` as-is, not referring to constant pool. It may lead to false-positive/negative outcomes when generated recordings are parsed well while the real ones make parser fail, or vice versa.
Is it worth to extend API to control which types must have constant pool and which must not? What do you think?

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PR: https://git.openjdk.java.net/jmc/pull/84