WhiteBox should provide an API for putting a concurrent GC into a specific phase and holding it there.  This is needed for writing tests that require the collector be in a particular phase when some test action is performed.
            
- blocks
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                    JDK-8166188 G1 Needs pre barrier on dereference of weak JNI handles -           
- Closed
 
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- relates to
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                    JDK-8240239 Replace ConcurrentGCPhaseManager -           
- Resolved
 
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                    JDK-8178813 Add test for G1 pre-barrier on dereference of weak JNI handles -           
- Resolved
 
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