Merge #6417: refactor: introduce cs_pendingSigns

397a157 refactor: introduce cs_pendingSigns (pasta)

Pull request description:

  ## Issue being fixed or feature implemented
  Much more minimal version of #6410; data from testnet while MNs were doing lots of instantsend locking showed minimal contention over signing_shares cs, however, the contention that did exist, most was a result of AsyncSign conflicting with something else. This should resolve the vast majority of contention in signing_shares while minimizing the complication / risk of introducing dead locks compared to 6410

  ## What was done?
  introduce cs_pendingSigns

  ## How Has This Been Tested?
  Built locally

  ## Breaking Changes
  None

  ## Checklist:
    _Go over all the following points, and put an `x` in all the boxes that apply._
  - [x] I have performed a self-review of my own code
  - [ ] I have commented my code, particularly in hard-to-understand areas
  - [ ] I have added or updated relevant unit/integration/functional/e2e tests
  - [ ] I have made corresponding changes to the documentation
  - [x] I have assigned this pull request to a milestone _(for repository code-owners and collaborators only)_

ACKs for top commit:
  knst:
    utACK 397a157
  UdjinM6:
    utACK 397a157

Tree-SHA512: aac741c274449cf9c22625ac95e964d275dd1454647eaa2fc064c90b44a215e5509c9f9b8aceccbd49002edc21cbea883900f202204aa2138c104f4989ae5e26

src/llmq/signing_shares.cpp

@@ -1479,15 +1479,15 @@ void CSigSharesManager::WorkThreadMain()
 
 void CSigSharesManager::AsyncSign(const CQuorumCPtr& quorum, const uint256& id, const uint256& msgHash)
 {
-    LOCK(cs);
+    LOCK(cs_pendingSigns);
     pendingSigns.emplace_back(quorum, id, msgHash);
 }
 
 void CSigSharesManager::SignPendingSigShares()
 {
     std::vector<PendingSignatureData> v;
     {
-        LOCK(cs);
+        LOCK(cs_pendingSigns);
         v = std::move(pendingSigns);
     }
 

src/llmq/signing_shares.h

@@ -399,7 +399,8 @@ class CSigSharesManager : public CRecoveredSigsListener
         PendingSignatureData(CQuorumCPtr quorum, const uint256& id, const uint256& msgHash) : quorum(std::move(quorum)), id(id), msgHash(msgHash){}
     };
 
-    std::vector<PendingSignatureData> pendingSigns GUARDED_BY(cs);
+    Mutex cs_pendingSigns;
+    std::vector<PendingSignatureData> pendingSigns GUARDED_BY(cs_pendingSigns);
 
     FastRandomContext rnd GUARDED_BY(cs);