From 44d1dbfbb8a2480a115877ba19a6c4a49757184b Mon Sep 17 00:00:00 2001
From: Michael Peter Christen <mc@yacy.net>
Date: Sun, 8 Feb 2026 13:34:17 +0100
Subject: fix for NetworkPicture not giving away sync release

---
 source/net/yacy/htroot/NetworkPicture.java | 107 +++++++++++++++--------------
 1 file changed, 57 insertions(+), 50 deletions(-)

diff --git a/source/net/yacy/htroot/NetworkPicture.java b/source/net/yacy/htroot/NetworkPicture.java
index 698331c89..0ebfb7f91 100644
--- a/source/net/yacy/htroot/NetworkPicture.java
+++ b/source/net/yacy/htroot/NetworkPicture.java
@@ -44,37 +44,41 @@ public class NetworkPicture {
     private static final Semaphore sync = new Semaphore(1, true);
     private static long lastAccessSeconds = 0;
 
-    public static EncodedImage respond(
-        final RequestHeader header,
-        final serverObjects post,
-        final serverSwitch env) {
-        final Switchboard sb = (Switchboard) env;
-        final boolean authorized = sb.adminAuthenticated(header) >= 2;
-
-        final long timeSeconds = System.currentTimeMillis() / 1000;
-        if (NetworkGraph.buffer != null && !authorized && timeSeconds - lastAccessSeconds < 2) {
-            if (log.isFine()) log.fine("cache hit (1); authorized = "
-                + authorized
-                + ", timeSeconds - lastAccessSeconds = "
-                + (timeSeconds - lastAccessSeconds));
-            return NetworkGraph.buffer;
-        }
-
-        if ( NetworkGraph.buffer != null && sync.availablePermits() == 0 ) {
-            return NetworkGraph.buffer;
-        }
-        sync.acquireUninterruptibly();
-
-        if (NetworkGraph.buffer != null && !authorized && timeSeconds - lastAccessSeconds < 2) {
-            if (log.isFine()) log.fine("cache hit (2); authorized = "
-                + authorized
-                + ", timeSeconds - lastAccessSeconds = "
-                + (timeSeconds - lastAccessSeconds));
-            sync.release();
-            return NetworkGraph.buffer;
-        }
-
-        int width = 1280; // 640x480 = VGA, 768x576 = SD/4:3, 1024x576 =SD/16:9 1280x720 = HD/16:9, 1920x1080 = FULL HD/16:9
+    public static EncodedImage respond(
+        final RequestHeader header,
+        final serverObjects post,
+        final serverSwitch env) {
+        final Switchboard sb = (Switchboard) env;
+        final boolean authorized = sb.adminAuthenticated(header) >= 2;
+
+        final long timeSeconds = System.currentTimeMillis() / 1000;
+        if (NetworkGraph.buffer != null && timeSeconds - lastAccessSeconds < 2) {
+            if (log.isFine()) log.fine("cache hit (1); authorized = "
+                + authorized
+                + ", timeSeconds - lastAccessSeconds = "
+                + (timeSeconds - lastAccessSeconds));
+            return NetworkGraph.buffer;
+        }
+
+        boolean lockAcquired = sync.tryAcquire();
+        if (!lockAcquired) {
+            if (NetworkGraph.buffer != null) {
+                return NetworkGraph.buffer;
+            }
+            sync.acquireUninterruptibly();
+            lockAcquired = true;
+        }
+        try {
+            final long refreshCheckSeconds = System.currentTimeMillis() / 1000;
+            if (NetworkGraph.buffer != null && refreshCheckSeconds - lastAccessSeconds < 2) {
+                if (log.isFine()) log.fine("cache hit (2); authorized = "
+                    + authorized
+                    + ", timeSeconds - lastAccessSeconds = "
+                    + (refreshCheckSeconds - lastAccessSeconds));
+                return NetworkGraph.buffer;
+            }
+
+            int width = 1280; // 640x480 = VGA, 768x576 = SD/4:3, 1024x576 =SD/16:9 1280x720 = HD/16:9, 1920x1080 = FULL HD/16:9
         int height = 720;
         int passiveLimit = 1440; // minutes; 1440 = 1 day; 720 = 12 hours; 1440 = 24 hours, 10080 = 1 week;
         int potentialLimit = 1440;
@@ -111,20 +115,20 @@ public class NetworkPicture {
             maxCount = 10000;
         }
 
-        NetworkGraph.buffer =
-            new EncodedImage(NetworkGraph.getNetworkPicture(
-                sb.peers,
-                width,
-                height,
-                passiveLimit,
-                potentialLimit,
-                maxCount,
-                coronaangle,
-                communicationTimeout,
-                env.getConfig(SwitchboardConstants.NETWORK_NAME, "unspecified"),
-                env.getConfig("network.unit.description", "unspecified"),
-                Long.parseLong(bgcolor, 16),
-                cyc), "png", false);
+            NetworkGraph.buffer =
+                new EncodedImage(NetworkGraph.getNetworkPicture(
+                    sb.peers,
+                    width,
+                    height,
+                    passiveLimit,
+                    potentialLimit,
+                    maxCount,
+                    coronaangle,
+                    communicationTimeout,
+                    env.getConfig(SwitchboardConstants.NETWORK_NAME, "unspecified"),
+                    env.getConfig("network.unit.description", "unspecified"),
+                    Long.parseLong(bgcolor, 16),
+                    cyc), "png", false);
 
         /*
         NetworkGraph.buffer =
@@ -142,10 +146,13 @@ public class NetworkPicture {
                 Long.parseLong(bgcolor, 16),
                 cyc), "png", false);
          */
-        lastAccessSeconds = System.currentTimeMillis() / 1000;
-
-        sync.release();
-        return NetworkGraph.buffer;
-    }
+            lastAccessSeconds = System.currentTimeMillis() / 1000;
+            return NetworkGraph.buffer;
+        } finally {
+            if (lockAcquired) {
+                sync.release();
+            }
+        }
+    }
 
 }
-- 
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