Reduce contention in the selector pool

headius · headius · commit 2c11bc1d5486 · 2023-05-23T10:47:59.000-05:00
This moves the creation of a new selector outside of the sync section, to avoid blocking threads that are just trying to put a selector back when we are waiting to open a new one. This whole class could use some improvement using nonblocking collections, but this should help reduce contention for now. See #7805.
diff --git a/core/src/main/java/org/jruby/util/io/SelectorPool.java b/core/src/main/java/org/jruby/util/io/SelectorPool.java
@@ -74,7 +74,7 @@ public synchronized Selector get() throws IOException{
      * @return a java.nio.channels.Selector
      * @throws IOException if there's a problem opening a new selector
      */
-    public synchronized Selector get(SelectorProvider provider) throws IOException{
+    public Selector get(SelectorProvider provider) throws IOException{
         return retrieveFromPool(provider);
     }
 
@@ -125,11 +125,14 @@ public synchronized void cleanup() {
     }
 
     private Selector retrieveFromPool(SelectorProvider provider) throws IOException {
-        List<Selector> providerPool = pool.get(provider);
-        if (providerPool != null && !providerPool.isEmpty()) {
-            return providerPool.remove(providerPool.size() - 1);
+        synchronized (this) {
+            List<Selector> providerPool = pool.get(provider);
+            if (providerPool != null && !providerPool.isEmpty()) {
+                return providerPool.remove(providerPool.size() - 1);
+            }
         }
 
+        // otherwise just return a new one
         return SelectorFactory.openWithRetryFrom(null, provider);
     }
 

Original file line number	Diff line number	Diff line change
`@@ -74,7 +74,7 @@ public synchronized Selector get() throws IOException{`
`74`	`74`	`* @return a java.nio.channels.Selector`
`75`	`75`	`* @throws IOException if there's a problem opening a new selector`
`76`	`76`	`*/`
`77`		`- public synchronized Selector get(SelectorProvider provider) throws IOException{`
	`77`	`+ public Selector get(SelectorProvider provider) throws IOException{`
`78`	`78`	`return retrieveFromPool(provider);`
`79`	`79`	`}`
`80`	`80`
`@@ -125,11 +125,14 @@ public synchronized void cleanup() {`
`125`	`125`	`}`
`126`	`126`
`127`	`127`	`private Selector retrieveFromPool(SelectorProvider provider) throws IOException {`
`128`		`- List<Selector> providerPool = pool.get(provider);`
`129`		`- if (providerPool != null && !providerPool.isEmpty()) {`
`130`		`- return providerPool.remove(providerPool.size() - 1);`
	`128`	`+ synchronized (this) {`
	`129`	`+ List<Selector> providerPool = pool.get(provider);`
	`130`	`+ if (providerPool != null && !providerPool.isEmpty()) {`
	`131`	`+ return providerPool.remove(providerPool.size() - 1);`
	`132`	`+ }`
`131`	`133`	`}`
`132`	`134`
	`135`	`+ // otherwise just return a new one`
`133`	`136`	`return SelectorFactory.openWithRetryFrom(null, provider);`
`134`	`137`	`}`
`135`	`138`