RFR: 8033764: Remove the usage of StarTask from BufferingOopClosure
stefan.karlsson at oracle.com
Thu Feb 6 03:20:34 PST 2014
please review the following patch:
for the RFE:
This is a first step to simplify/unify the code root scanning, something
we want for the G1 Class Unloading project:
G1 uses the BufferingOopClosure to separate the root iteration from the
object copying. The oop*/narrowOop* roots are gathered in a buffer and
then bulk processed. By only timing the processing part and not the root
iteration, the object copying time can be measured.
Currently, the BufferingOopClosure uses StarTask, from the taskqueue
code, to differentiate between oop* and narrowOop* roots. The StarTask
uses the least significant bit to mark whether the address contains an
oop or a narrowOop. This works for most of the roots, since the
addresses are aligned and the LSB is always 0. However, oops can be
embedded as immediates in the JITed code and the addresses for these are
not necessarily aligned. This prevents us from using StarTasks with oops
in the CodeCache.
See this comment from g1_process_strong_roots:
// Walk the code cache/strong code roots w/o buffering, because StarTask
// cannot handle unaligned oop locations.
CodeBlobToOopClosure eager_scan_code_roots(scan_non_heap_roots, true /*
I suggest that we replace the StartTask usage with another
implementation that allows the BufferingOopClosures to be used for the
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