Instead of having a single NodeContext::shutdown member that is used both to
request shutdowns and check if they have been requested, use separate members
for each. Benefits of this change:
1. Should make code a little clearer and easier to search because it is easier
to see which parts of code are triggering shutdowns and which parts are just
checking to see if they were triggered.
2. Makes it possible for init.cpp to specify additional code to run when a
shutdown is requested, like signalling the m_tip_block_cv condition variable.
Motivation for this change was to remove hacky NodeContext argument and
m_tip_block_cv access from the StopRPC function, so StopRPC can just be
concerned with RPC functionality, not other node functionality.
The src/node/ directory contains code that needs to access node state
(state in CChain, CBlockIndex, CCoinsView, CTxMemPool, and similar
classes).
Code in src/node/ is meant to be segregated from code in
src/wallet/ and src/qt/, to ensure wallet and GUI
code changes don't interfere with node operation, to allow wallet and GUI code
to run in separate processes, and to perhaps eventually allow wallet and GUI
code to be maintained in separate source repositories.
As a rule of thumb, code in one of the src/node/,
src/wallet/, or src/qt/ directories should avoid
calling code in the other directories directly, and only invoke it indirectly
through the more limited src/interfaces/ classes.
This directory is at the moment
sparsely populated. Eventually more substantial files like
src/validation.cpp and
src/txmempool.cpp might be moved there.
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