RFR: 8255934: JConsole 14 and greater fails to connect to older JVM

[Chris Plummer]

On Mon, 16 Nov 2020 23:00:05 GMT, Alex Menkov <amenkov at openjdk.org> wrote:

> OperatingSystemMXBean was changed in jdk14 (see JDK-8226575):
> New methods getTotalMemorySize and getFreeMemorySize were added, old getTotalPhysicalMemorySize and getFreePhysicalMemorySize were deprecated.
> 
> The fix adds fallbacks for the values (i.e. if new methods fail, jconsole calls old methods)

src/jdk.jconsole/share/classes/sun/tools/jconsole/SummaryTab.java line 268:

> 266:                                                     sunOSMBean::getTotalPhysicalMemorySize),
> 267:                                            tryToGet(sunOSMBean::getFreeMemorySize,
> 268:                                                     sunOSMBean::getFreePhysicalMemorySize),

What happens if/when `getTotalPhysicalMemorySize()` and `getFreePhysicalMemorySize()` are removed. This code will fail to compile, right? I guess at that point the fix would be to try the new API, and if it throws an exception, then just use -1. In other words, there would be no way to get the value from older JVMs.

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PR: https://git.openjdk.java.net/jdk/pull/1243