JAVA-2859: Use current cluster description for server session pruning

By replacing a call to Cluster.getDescription to Cluster.getDescription
when evaluating whether to prune a server session, the driver avoids
potentially blocking and timing out if the cluster description is
unavailable (as when it loses connections to all servers in the cluster)

Author: jyemin

driver-core/src/main/com/mongodb/internal/session/ServerSessionPool.java

@@ -132,7 +132,8 @@ private void endClosedSessions() {
     }
 
     private boolean shouldPrune(final ServerSessionImpl serverSession) {
-        Integer logicalSessionTimeoutMinutes = cluster.getDescription().getLogicalSessionTimeoutMinutes();
+        Integer logicalSessionTimeoutMinutes = cluster.getCurrentDescription().getLogicalSessionTimeoutMinutes();
+        // if the server no longer supports sessions, prune the session
         if (logicalSessionTimeoutMinutes == null) {
             return false;
         }

driver-core/src/test/unit/com/mongodb/internal/session/ServerSessionPoolSpecification.groovy

@@ -67,7 +67,7 @@ class ServerSessionPoolSpecification extends Specification {
     def 'should get session'() {
         given:
         def cluster = Stub(Cluster) {
-            getDescription() >> connectedDescription
+            getCurrentDescription() >> connectedDescription
         }
         def pool = new ServerSessionPool(cluster)
 
@@ -81,7 +81,7 @@ class ServerSessionPoolSpecification extends Specification {
     def 'should throw IllegalStateException if pool is closed'() {
         given:
         def cluster = Stub(Cluster) {
-            getDescription() >> connectedDescription
+            getCurrentDescription() >> connectedDescription
         }
         def pool = new ServerSessionPool(cluster)
         pool.close()
@@ -97,7 +97,7 @@ class ServerSessionPoolSpecification extends Specification {
     def 'should pool session'() {
         given:
         def cluster = Stub(Cluster) {
-            getDescription() >> connectedDescription
+            getCurrentDescription() >> connectedDescription
         }
         def pool = new ServerSessionPool(cluster)
         def session = pool.get()
@@ -113,7 +113,7 @@ class ServerSessionPoolSpecification extends Specification {
     def 'should prune sessions on release'() {
         given:
         def cluster = Mock(Cluster) {
-            getDescription() >> connectedDescription
+            getCurrentDescription() >> connectedDescription
         }
         def clock = Stub(ServerSessionPool.Clock) {
             millis() >>> [0, 0,                          // first get
@@ -157,7 +157,7 @@ class ServerSessionPoolSpecification extends Specification {
     def 'should prune sessions when getting'() {
         given:
         def cluster = Mock(Cluster) {
-            getDescription() >> connectedDescription
+            getCurrentDescription() >> connectedDescription
         }
         def clock = Stub(ServerSessionPool.Clock) {
             millis() >>> [0, 0,                          // first get
@@ -186,11 +186,10 @@ class ServerSessionPoolSpecification extends Specification {
     def 'should not prune session when timeout is null'() {
         given:
         def cluster = Stub(Cluster) {
-            getDescription() >> unconnectedDescription
+            getCurrentDescription() >> unconnectedDescription
         }
         def clock = Stub(ServerSessionPool.Clock) {
-            millis() >>> [0, 0,
-                          MINUTES.toMillis(29) + 1]
+            millis() >>> [0, 0, 0]
         }
         def pool = new ServerSessionPool(cluster, clock)
         def session = pool.get()
@@ -207,7 +206,7 @@ class ServerSessionPoolSpecification extends Specification {
     def 'should initialize session'() {
         given:
         def cluster = Stub(Cluster) {
-            getDescription() >> connectedDescription
+            getCurrentDescription() >> connectedDescription
         }
         def clock = Stub(ServerSessionPool.Clock) {
             millis() >> 42
@@ -235,7 +234,7 @@ class ServerSessionPoolSpecification extends Specification {
             getConnection() >> connection
         }
         def cluster = Mock(Cluster) {
-            getDescription() >> connectedDescription
+            getCurrentDescription() >> connectedDescription
         }
         def pool = new ServerSessionPool(cluster)
         // check out sessions up the the endSessions batch size