From a6d24b3ac1d0416847dddbfd686e953552ca68f6 Mon Sep 17 00:00:00 2001
From: Tor Brede Vekterli <vekterli@yahooinc.com>
Date: Tue, 17 Oct 2023 15:51:30 +0000
Subject: Use `shared_mutex` to allow non-contending reads (common case)

---
 .../vespa/documentapi/messagebus/policies/contentpolicy.cpp    | 10 +++++-----
 .../src/vespa/documentapi/messagebus/policies/contentpolicy.h  |  4 ++--
 2 files changed, 7 insertions(+), 7 deletions(-)

(limited to 'documentapi/src')

diff --git a/documentapi/src/vespa/documentapi/messagebus/policies/contentpolicy.cpp b/documentapi/src/vespa/documentapi/messagebus/policies/contentpolicy.cpp
index c13f32f2df5..ea27d42e790 100644
--- a/documentapi/src/vespa/documentapi/messagebus/policies/contentpolicy.cpp
+++ b/documentapi/src/vespa/documentapi/messagebus/policies/contentpolicy.cpp
@@ -103,7 +103,7 @@ void
 ContentPolicy::configure(std::unique_ptr<vespa::config::content::StorDistributionConfig> config)
 {
     try {
-        std::lock_guard guard(_lock);
+        std::lock_guard guard(_rw_lock);
         _distribution = std::make_unique<storage::lib::Distribution>(*config);
     } catch (const std::exception& e) {
         LOG(warning, "Got exception when configuring distribution, config id was %s", _clusterConfigId.c_str());
@@ -235,7 +235,7 @@ void
 ContentPolicy::updateStateFromReply(WrongDistributionReply& wdr)
 {
     auto newState = std::make_unique<storage::lib::ClusterState>(wdr.getSystemState());
-    std::lock_guard guard(_lock);
+    std::lock_guard guard(_rw_lock);
     if (!_state || newState->getVersion() >= _state->getVersion()) {
         if (_state) {
             wdr.getTrace().trace(1, make_string("System state changed from version %u to %u",
@@ -256,14 +256,14 @@ ContentPolicy::updateStateFromReply(WrongDistributionReply& wdr)
 ContentPolicy::StateSnapshot
 ContentPolicy::internal_state_snapshot()
 {
-    std::lock_guard guard(_lock);
+    std::shared_lock guard(_rw_lock);
     return {_state, _distribution};
 }
 
 std::shared_ptr<const storage::lib::ClusterState>
 ContentPolicy::getSystemState() const noexcept
 {
-    std::lock_guard guard(_lock);
+    std::shared_lock guard(_rw_lock);
     return _state;
 }
 
@@ -273,7 +273,7 @@ ContentPolicy::reset_state()
     // It's possible for the caller to race between checking and resetting the state,
     // but this should never lead to a worse outcome than sending to a random distributor
     // as if no state had been cached prior.
-    std::lock_guard guard(_lock);
+    std::lock_guard guard(_rw_lock);
     _state.reset();
 }
 
diff --git a/documentapi/src/vespa/documentapi/messagebus/policies/contentpolicy.h b/documentapi/src/vespa/documentapi/messagebus/policies/contentpolicy.h
index 182b35a0e98..7a3675c3001 100644
--- a/documentapi/src/vespa/documentapi/messagebus/policies/contentpolicy.h
+++ b/documentapi/src/vespa/documentapi/messagebus/policies/contentpolicy.h
@@ -6,7 +6,7 @@
 #include <vespa/vdslib/distribution/distribution.h>
 #include <vespa/document/bucket/bucketidfactory.h>
 #include <vespa/messagebus/routing/hop.h>
-#include <mutex>
+#include <shared_mutex>
 
 namespace config {
     class ICallback;
@@ -24,7 +24,7 @@ class ContentPolicy : public ExternSlobrokPolicy
 {
 private:
     document::BucketIdFactory                         _bucketIdFactory;
-    mutable std::mutex                                _lock;
+    mutable std::shared_mutex                         _rw_lock;
     std::shared_ptr<const storage::lib::ClusterState> _state;
     string                                            _clusterName;
     string                                            _clusterConfigId;
-- 
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