Replace synchronized block with ReentrantLock (#208)

Replace synchronized block with ReentrantLock to avoid possible thread pinning with VirtualThreads (Java 21)
mweirauch · Sep 8, 2024 · 4cba70e · 4cba70e
1 parent 2cd444f
commit 4cba70e
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Showing 2 changed files with 12 additions and 4 deletions.
diff --git a/src/main/java/io/github/mweirauch/micrometer/jvm/extras/procfs/ProcfsEntry.java b/src/main/java/io/github/mweirauch/micrometer/jvm/extras/procfs/ProcfsEntry.java
@@ -20,6 +20,7 @@
 import java.util.Map;
 import java.util.Objects;
 
+import java.util.concurrent.locks.ReentrantLock;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -29,7 +30,7 @@ abstract class ProcfsEntry {
 
     private static final long CACHE_DURATION_MS = 1000;
 
-    private final Object lock = new Object();
+    private final ReentrantLock lock = new ReentrantLock();
 
     private final ProcfsReader reader;
 
@@ -58,7 +59,8 @@ public Double get(ValueKey key) {
         if (lastHandle != -1 && lastHandle + CACHE_DURATION_MS > currentTime()) {
             return;
         }
-        synchronized (lock) {
+        try {
+            lock.lock();
             if (lastHandle != -1 && lastHandle + CACHE_DURATION_MS > currentTime()) {
                 return;
             }
@@ -73,6 +75,8 @@ public Double get(ValueKey key) {
                 values.clear();
                 log.warn("Failed reading '" + reader.getEntryPath() + "'!", e);
             }
+        } finally {
+            lock.unlock();
         }
     }
 

diff --git a/src/main/java/io/github/mweirauch/micrometer/jvm/extras/procfs/ProcfsReader.java b/src/main/java/io/github/mweirauch/micrometer/jvm/extras/procfs/ProcfsReader.java
@@ -24,6 +24,7 @@
 import java.util.Locale;
 import java.util.Map;
 import java.util.Objects;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.function.Consumer;
 
 import org.slf4j.Logger;
@@ -35,7 +36,7 @@ class ProcfsReader {
 
     private static final Map<String, ProcfsReader> instances = new HashMap<>();
 
-    private static final Object instancesLock = new Object();
+    private static final ReentrantLock instancesLock = new ReentrantLock();
 
     private static final Path BASE = Paths.get("/proc", "self");
 
@@ -93,8 +94,11 @@ private void readPath(Path path, Consumer<String> consumer) throws IOException {
     /* default */ static ProcfsReader getInstance(String entry) {
         Objects.requireNonNull(entry);
 
-        synchronized (instancesLock) {
+        try {
+            instancesLock.lock();
             return instances.computeIfAbsent(entry, e -> new ProcfsReader(e));
+        } finally{
+            instancesLock.unlock();
         }
     }