6875716: JLayer.remove((Component)null) should behave consistently in (not) throwing NPE
Reviewed-by: rupashka
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<title>
SA HSDB GUI
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<p>
Once the HSDB debugger has been launched, the threads list is displayed
if launched with debuggee options (pid or core) in command line. If
HSDB was launched without debuggee, empty screen is shown.
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<p>File menu sub-menu options to attach, detach debuggee and exit tool.</p>
<p>Tools menu sub-menus include:</p>
<ul>
<li>browsing of the annotated stack memory ("Stack Memory" button). It
is currently annotated with the following information:
<ul>
<li> method names of the Java frames and their extents (supporting
inlined compiled methods)
<li> locations and types of oops, found using the oop map information
from compiled methods (interpreter oop maps coming soon)
<li> if a Java frame was interrupted by a signal (e.g., because of a
crash), annotates the frame with the signal name and number
<li> interpreter codelet descriptions for interpreted frames
</ul>
<li> finding which thread or threads caused a crash (currently
identified by the presence of a signal handler frame - solaris-only)
<li> browsing of oops using the Oop Inspector.
<li> browsing of the java.lang.Thread object's oop.
<li> Object Histogram and inspection of objects and liveness analysis therein.
<li> Class Browser - view Java classes, bytecode disassembly,
or create .class files for selected classes
<li> native disassembly (sparc, x86 only) and nmethod disassembly with annotations for safepoint details.
<li> view -XX flags, System properties, VM version of debuggee
</ul>
<p>Windows sub-menu options include:</p>
<ul>
<li> Windows sub-menu: Console window to run "CLHSDB" commands in GUI
<li> Windows sub-menu: Debugger console of underlying native debugger (MS Windbg or dbx (if used))
</ul>
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