RFR: 8301639: JDI and JDWP specs should clarify potential deadlock issues with method invocation

[Chris Plummer]

On Wed, 13 Sep 2023 12:47:48 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> This PR includes a couple of clarifications of the JDWP and JDI invoke method support. The first is that deadlocks can occur due to a needed "resource" being held. The spec previously just mentioned monitors being held, but this is too specific. The second is to clarify that an invoke on a virtual thread can be more prone to deadlocks than a platform thread may be.
>> 
>> I did a doc build you can look at to view the changes. Links to the relevant sections are below:
>> 
>> https://cr.openjdk.org/~cjplummer/8301639/docs.00/specs/jdwp/jdwp-protocol.html#JDWP_ClassType_InvokeMethod
>> 
>> https://cr.openjdk.org/~cjplummer/8301639/docs.00/specs/jdwp/jdwp-protocol.html#JDWP_ClassType_NewInstance
>> 
>> https://cr.openjdk.org/~cjplummer/8301639/docs.00/specs/jdwp/jdwp-protocol.html#JDWP_InterfaceType_InvokeMethod
>> 
>> https://cr.openjdk.org/~cjplummer/8301639/docs.00/specs/jdwp/jdwp-protocol.html#JDWP_ObjectReference_InvokeMethod
>> 
>> https://cr.openjdk.org/~cjplummer/8301639/docs.00/api/jdk.jdi/com/sun/jdi/ClassType.html#invokeMethod(com.sun.jdi.ThreadReference,com.sun.jdi.Method,java.util.List,int)
>> 
>> https://cr.openjdk.org/~cjplummer/8301639/docs.00/api/jdk.jdi/com/sun/jdi/ClassType.html#newInstance(com.sun.jdi.ThreadReference,com.sun.jdi.Method,java.util.List,int)
>> 
>> https://cr.openjdk.org/~cjplummer/8301639/docs.00/api/jdk.jdi/com/sun/jdi/InterfaceType.html#invokeMethod(com.sun.jdi.ThreadReference,com.sun.jdi.Method,java.util.List,int)
>> 
>> https://cr.openjdk.org/~cjplummer/8301639/docs.00/api/jdk.jdi/com/sun/jdi/ObjectReference.html#invokeMethod(com.sun.jdi.ThreadReference,com.sun.jdi.Method,java.util.List,int)
>
> src/java.se/share/data/jdwp/jdwp.spec line 1150:
> 
>> 1148:         "suspended by an event or by command. "
>> 1149:         "This is done to prevent the deadlocks "
>> 1150:         "that will occur if any of the threads own resources, such as monitors, "
> 
> In passing, shouldn't that be "may occur" rather than the "will occur"? (the full context isn't visible here so it's hard to see).

No, because the line below follows with "...that _will_ be needed by the invoked method". If the resource _will_ be needed, then the deadlock _will_ occur.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15695#discussion_r1324741135