Determining if JVMCI is enabled and whether it is being used by the JVM

[Doug Simon]

Here’s some useful information on how to be able to query this kind of information from Java.

> Begin forwarded message:
> 
> From: Roland Schatz <roland.schatz at oracle.com>
> Subject: Re: Problems building Graal-0.12 on Debian 8
> Date: 28 June 2016 at 13:23:19 GMT+2
> 
> It depends on what exactly you want to know:
> 
> - Am I running a JDK that supports JVMCI?
> Look at the "java.vm.version" system property.
> On JDK 8, it will contain "jvmci-<version>" for jvmci-enabled builds.
> JDK 9 always has JVMCI built in.
> 
> - Is JVMCI enabled and/or used?
> For that, you can query the VM options (EnableJVMCI and UseJVMCICompiler) using the management API.
> 
> - What compiler is selected?
> That's in the "jvmci.Compiler" system property.
> 
>> import java.lang.management.ManagementFactory;
>> import com.sun.management.HotSpotDiagnosticMXBean;
>> import com.sun.management.VMOption;
>> 
>> class JVMCIQuery {
>>    public static void main(String[] args) {
>>        // Am I running on a JDK that supports JVMCI?
>>        String vm_version = System.getProperty("java.vm.version");
>>        System.out.printf("java.vm.version = %s%n", vm_version);
>> 
>>        HotSpotDiagnosticMXBean bean = ManagementFactory.getPlatformMXBean(HotSpotDiagnosticMXBean.class);
>> 
>>        // Is JVMCI enabled?
>>        VMOption enableJVMCI = bean.getVMOption("EnableJVMCI");
>>        System.out.println(enableJVMCI);
>> 
>>        // Is the system using the JVMCI compiler for normal compilations?
>>        VMOption useJVMCICompiler = bean.getVMOption("UseJVMCICompiler");
>>        System.out.println(useJVMCICompiler);
>> 
>>        // What compiler is selected?
>>        String compiler = System.getProperty("jvmci.Compiler");
>>        System.out.printf("jvmci.Compiler = %s%n", compiler);
>>    }
>> }
> 
> On a normal JDK 8 (without JVMCI), you'll get:
> 
> [roland at oracle-rs graal-core]$ java -cp graal_fun JVMCIQuery
> java.vm.version = 25.92-b14
> Exception in thread "main" java.lang.IllegalArgumentException: VM option "EnableJVMCI" does not exist
>        at sun.management.HotSpotDiagnostic.getVMOption(HotSpotDiagnostic.java:73)
>        at JVMCIQuery.main(JVMCIQuery.java:12)
> 
> 
> On a JDK 8 with JVMCI (i.e. JVMCI enabled, but not used by default):
> 
> [roland at oracle-rs graal-core]$ mx vm -cp graal_fun JVMCIQuery
> java.vm.version = 25.71-b01-internal-jvmci-0.17-dev
> VM option: EnableJVMCI value: true  origin: VM_CREATION (read-only)
> VM option: UseJVMCICompiler value: false  origin: DEFAULT (read-only)
> jvmci.Compiler = graal
> 
> 
> On a JDK 8 with JVMCI, using Graal as the system compiler:
> 
> [roland at oracle-rs graal-core]$ mx vm -cp graal_fun -XX:+UseJVMCICompiler JVMCIQuery
> java.vm.version = 25.71-b01-internal-jvmci-0.17-dev
> VM option: EnableJVMCI value: true  origin: VM_CREATION (read-only)
> VM option: UseJVMCICompiler value: true  origin: VM_CREATION (read-only)
> jvmci.Compiler = graal
> 
> 
> - Roland