RFR (S): 8228858: Reimplement JVM_RawMonitors to use PlatformMutex

[David Holmes]

One follow up to clarify testing ...

On 14/08/2019 10:32 pm, David Holmes wrote:
> bug: https://bugs.openjdk.java.net/browse/JDK-8228858
> webrev: http://cr.openjdk.java.net/~dholmes/8228858/webrev/
> 
> A JVM_RawMonitor  (not to be confused with JvmtiRawMonitor) is a simple 
> mutex (despite the name) currently implemented via two special entry 
> points in the VM Monitor code. This fix changes that so that a 
> JVM_RawMonitor is just a PlatformMutex, enabling us to delete the 
> special Monitor code.
> 
> There are two clients of JVM_RawMonitor:
> - the native Zip library provided by the JDK and used by the JVM during 
> classloading
> - AWT debug code
> 
> The first should be tested by using the VM. :) The second I don't know. 
> But the functionality we're testing is already present so there's 
> sufficient coverage just by testing one client.

That may have sounded a bit too much like "fingers crossed it should be 
okay" :)

In essence this change introduces no new code, it just shortens the code 
paths. E.g for locking

Current:

JVM_RawMonitorLock -> Monitor::raw_enter -> PlatformMonitor::lock -> 
pthread_mutex_lock

New:

JVM_RawMonitorLock -> PlatformMutex::lock -> pthread_mutex_lock

we are just cutting out the indirection via the Monitor class.

David
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> Testing: tiers 1 - 3 on Linux/macOS/Window x64, Solaris sparcv9
> 
> Thanks,
> David