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[net processing] Improve documentation for Peer destruction/locking

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Suggested here:

- https://github.com/bitcoin/bitcoin/pull/19607#discussion_r467071878
- https://github.com/bitcoin/bitcoin/pull/19829#discussion_r546116786
This commit is contained in:
John Newbery 2020-08-28 21:04:44 +01:00
parent f1dbf92ff0
commit 717a374e74
2 changed files with 9 additions and 1 deletions
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5
src/net_processing.cpp
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@ -791,6 +791,11 @@ void PeerManager::FinalizeNode(const CNode& node, bool& fUpdateConnectionTime) {
LOCK(cs_main); LOCK(cs_main);
int misbehavior{0}; int misbehavior{0};
{ {
// We remove the PeerRef from g_peer_map here, but we don't always
// destruct the Peer. Sometimes another thread is still holding a
// PeerRef, so the refcount is >= 1. Be careful not to do any
// processing here that assumes Peer won't be changed before it's
// destructed.
PeerRef peer = RemovePeer(nodeid); PeerRef peer = RemovePeer(nodeid);
assert(peer != nullptr); assert(peer != nullptr);
misbehavior = WITH_LOCK(peer->m_misbehavior_mutex, return peer->m_misbehavior_score); misbehavior = WITH_LOCK(peer->m_misbehavior_mutex, return peer->m_misbehavior_score);

5
src/net_processing.h
View File

@ -46,6 +46,8 @@ struct CNodeStateStats {
* Memory is owned by shared pointers and this object is destructed when * Memory is owned by shared pointers and this object is destructed when
* the refcount drops to zero. * the refcount drops to zero.
* *
* Mutexes inside this struct must not be held when locking m_peer_mutex.
*
* TODO: move most members from CNodeState to this structure. * TODO: move most members from CNodeState to this structure.
* TODO: move remaining application-layer data members from CNode to this structure. * TODO: move remaining application-layer data members from CNode to this structure.
*/ */
@ -210,7 +212,8 @@ private:
* on extra block-relay-only peers. */ * on extra block-relay-only peers. */
bool m_initial_sync_finished{false}; bool m_initial_sync_finished{false};
/** Protects m_peer_map */ /** Protects m_peer_map. This mutex must not be locked while holding a lock
* on any of the mutexes inside a Peer object. */
mutable Mutex m_peer_mutex; mutable Mutex m_peer_mutex;
/** /**
* Map of all Peer objects, keyed by peer id. This map is protected * Map of all Peer objects, keyed by peer id. This map is protected