(coordination) Trial the use of zookeeper for coordinating semaphores across multiple crawler-like processes

The performance implication of this needs to be evaluated.  If it does not hold water. some other solution may be required instead.

code/common/service/java/nu/marginalia/service/discovery/ServiceRegistryIf.java

@@ -5,12 +5,10 @@ import nu.marginalia.service.discovery.monitor.ServiceChangeMonitor;
 import nu.marginalia.service.discovery.monitor.ServiceMonitorIf;
 import nu.marginalia.service.discovery.property.ServiceEndpoint;
 import nu.marginalia.service.discovery.property.ServiceKey;
+import org.apache.curator.framework.recipes.locks.InterProcessSemaphoreV2;
 
-import java.util.Collection;
 import java.util.List;
 import java.util.UUID;
-import java.util.function.BiConsumer;
-import java.util.function.Consumer;
 
 import static nu.marginalia.service.discovery.property.ServiceEndpoint.InstanceAddress;
 
@@ -66,6 +64,6 @@ public interface ServiceRegistryIf {
 
     void registerProcess(String processName, int nodeId);
     void deregisterProcess(String processName, int nodeId);
-    void watchProcess(String processName, int nodeId, Consumer<Boolean> callback) throws Exception;
+
-    void watchProcessAnyNode(String processName, Collection<Integer> nodes, BiConsumer<Boolean, Integer> callback) throws Exception;
+    InterProcessSemaphoreV2 getSemaphore(String name, int permits) throws Exception;
 }

code/common/service/java/nu/marginalia/service/discovery/ZkServiceRegistry.java

@@ -6,6 +6,7 @@ import nu.marginalia.service.discovery.monitor.ServiceMonitorIf;
 import nu.marginalia.service.discovery.property.ServiceEndpoint;
 import nu.marginalia.service.discovery.property.ServiceKey;
 import org.apache.curator.framework.CuratorFramework;
+import org.apache.curator.framework.recipes.locks.InterProcessSemaphoreV2;
 import org.apache.curator.utils.ZKPaths;
 import org.apache.zookeeper.CreateMode;
 import org.apache.zookeeper.Watcher;
@@ -13,10 +14,11 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import java.nio.charset.StandardCharsets;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Random;
+import java.util.UUID;
 import java.util.concurrent.TimeUnit;
-import java.util.function.BiConsumer;
-import java.util.function.Consumer;
 
 import static nu.marginalia.service.discovery.property.ServiceEndpoint.InstanceAddress;
 
@@ -283,60 +285,12 @@ public class ZkServiceRegistry implements ServiceRegistryIf {
     }
 
     @Override
-    public void watchProcess(String processName, int nodeId, Consumer<Boolean> callback) throws Exception {
+    public InterProcessSemaphoreV2 getSemaphore(String name, int permits) {
-        String path = "/process-locks/" + processName + "/" + nodeId;
+        if (stopped)
+            throw new IllegalStateException("Service registry is stopped, cannot get semaphore " + name);
 
-        // first check if the path exists and call the callback accordingly
+        String path = "/semaphores/" + name;
-
+        return new InterProcessSemaphoreV2(curatorFramework, path, permits);
-        if (curatorFramework.checkExists().forPath(path) != null) {
-            callback.accept(true);
-        }
-        else {
-            callback.accept(false);
-        }
-
-        curatorFramework.watchers().add()
-                .usingWatcher((Watcher) change -> {
-                    Watcher.Event.EventType type = change.getType();
-
-                    if (type == Watcher.Event.EventType.NodeCreated) {
-                        callback.accept(true);
-                    }
-                    if (type == Watcher.Event.EventType.NodeDeleted) {
-                        callback.accept(false);
-                    }
-                })
-                .forPath(path);
-
-    }
-
-    @Override
-    public void watchProcessAnyNode(String processName, Collection<Integer> nodes, BiConsumer<Boolean, Integer> callback) throws Exception {
-
-        for (int node : nodes) {
-            String path = "/process-locks/" + processName + "/" + node;
-
-            // first check if the path exists and call the callback accordingly
-            if (curatorFramework.checkExists().forPath(path) != null) {
-                callback.accept(true, node);
-            }
-            else {
-                callback.accept(false, node);
-            }
-
-            curatorFramework.watchers().add()
-                    .usingWatcher((Watcher) change -> {
-                        Watcher.Event.EventType type = change.getType();
-
-                        if (type == Watcher.Event.EventType.NodeCreated) {
-                            callback.accept(true, node);
-                        }
-                        if (type == Watcher.Event.EventType.NodeDeleted) {
-                            callback.accept(false, node);
-                        }
-                    })
-                    .forPath(path);
-        }
     }
 
     /* Exposed for tests */

code/functions/live-capture/build.gradle

@@ -22,6 +22,7 @@ dependencies {
     implementation project(':code:common:db')
     implementation project(':code:libraries:blocking-thread-pool')
     implementation project(':code:libraries:message-queue')
+    implementation project(':code:libraries:domain-lock')
 
     implementation project(':code:execution:api')
     implementation project(':code:processes:crawling-process:ft-content-type')

code/functions/live-capture/java/nu/marginalia/rss/svc/DomainLocks.java

@@ -1,66 +0,0 @@
-package nu.marginalia.rss.svc;
-
-import nu.marginalia.model.EdgeDomain;
-
-import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.Semaphore;
-
-/** Holds lock objects for each domain, to prevent multiple threads from
- * crawling the same domain at the same time.
- */
-public class DomainLocks {
-    // The locks are stored in a map, with the domain name as the key.  This map will grow
-    // relatively big, but should be manageable since the number of domains is limited to
-    // a few hundred thousand typically.
-    private final Map<String, Semaphore> locks = new ConcurrentHashMap<>();
-
-    /** Returns a lock object corresponding to the given domain.  The object is returned as-is,
-     * and may be held by another thread.  The caller is responsible for locking and  releasing the lock.
-     */
-    public DomainLock lockDomain(EdgeDomain domain) throws InterruptedException {
-        return new DomainLock(domain.toString(),
-                locks.computeIfAbsent(domain.topDomain.toLowerCase(), this::defaultPermits));
-    }
-
-    private Semaphore defaultPermits(String topDomain) {
-        if (topDomain.equals("wordpress.com"))
-            return new Semaphore(16);
-        if (topDomain.equals("blogspot.com"))
-            return new Semaphore(8);
-
-        if (topDomain.equals("neocities.org"))
-            return new Semaphore(4);
-        if (topDomain.equals("github.io"))
-            return new Semaphore(4);
-
-        if (topDomain.equals("substack.com")) {
-            return new Semaphore(1);
-        }
-        if (topDomain.endsWith(".edu")) {
-            return new Semaphore(1);
-        }
-
-        return new Semaphore(2);
-    }
-
-    public static class DomainLock implements AutoCloseable {
-        private final String domainName;
-        private final Semaphore semaphore;
-
-        DomainLock(String domainName, Semaphore semaphore) throws InterruptedException {
-            this.domainName = domainName;
-            this.semaphore = semaphore;
-
-            Thread.currentThread().setName("fetching:" + domainName + " [await domain lock]");
-            semaphore.acquire();
-            Thread.currentThread().setName("fetching:" + domainName);
-        }
-
-        @Override
-        public void close() {
-            semaphore.release();
-            Thread.currentThread().setName("fetching:" + domainName + " [wrapping up]");
-        }
-    }
-}

code/functions/live-capture/java/nu/marginalia/rss/svc/FeedFetcherService.java

@@ -5,6 +5,8 @@ import com.opencsv.CSVReader;
 import nu.marginalia.WmsaHome;
 import nu.marginalia.contenttype.ContentType;
 import nu.marginalia.contenttype.DocumentBodyToString;
+import nu.marginalia.coordination.DomainCoordinator;
+import nu.marginalia.coordination.DomainLock;
 import nu.marginalia.executor.client.ExecutorClient;
 import nu.marginalia.model.EdgeDomain;
 import nu.marginalia.nodecfg.NodeConfigurationService;
@@ -51,12 +53,13 @@ public class FeedFetcherService {
     private final ServiceHeartbeat serviceHeartbeat;
     private final ExecutorClient executorClient;
 
-    private final DomainLocks domainLocks = new DomainLocks();
+    private final DomainCoordinator domainCoordinator;
 
     private volatile boolean updating;
 
     @Inject
     public FeedFetcherService(FeedDb feedDb,
+                              DomainCoordinator domainCoordinator,
                               FileStorageService fileStorageService,
                               NodeConfigurationService nodeConfigurationService,
                               ServiceHeartbeat serviceHeartbeat,
@@ -67,6 +70,7 @@ public class FeedFetcherService {
         this.nodeConfigurationService = nodeConfigurationService;
         this.serviceHeartbeat = serviceHeartbeat;
         this.executorClient = executorClient;
+        this.domainCoordinator = domainCoordinator;
     }
 
     public enum UpdateMode {
@@ -132,7 +136,7 @@ public class FeedFetcherService {
                         };
 
                         FetchResult feedData;
-                        try (DomainLocks.DomainLock domainLock = domainLocks.lockDomain(new EdgeDomain(feed.domain()))) {
+                        try (DomainLock domainLock = domainCoordinator.lockDomain(new EdgeDomain(feed.domain()))) {
                             feedData = fetchFeedData(feed, client, fetchExecutor, ifModifiedSinceDate, ifNoneMatchTag);
                         } catch (Exception ex) {
                             feedData = new FetchResult.TransientError();

code/libraries/domain-lock/build.gradle

@@ -0,0 +1,32 @@
+plugins {
+    id 'java'
+}
+
+java {
+    toolchain {
+        languageVersion.set(JavaLanguageVersion.of(rootProject.ext.jvmVersion))
+    }
+}
+
+apply from: "$rootProject.projectDir/srcsets.gradle"
+
+dependencies {
+    implementation libs.bundles.slf4j
+    implementation project(':code:common:model')
+    implementation project(':code:common:config')
+    implementation project(':code:common:service')
+
+    implementation libs.bundles.curator
+
+    implementation libs.guava
+    implementation dependencies.create(libs.guice.get()) {
+        exclude group: 'com.google.guava'
+    }
+    testImplementation libs.bundles.slf4j.test
+    testImplementation libs.bundles.junit
+    testImplementation libs.mockito
+}
+
+test {
+    useJUnitPlatform()
+}

code/libraries/domain-lock/java/nu/marginalia/coordination/DefaultDomainPermits.java

@@ -0,0 +1,32 @@
+package nu.marginalia.coordination;
+
+import nu.marginalia.model.EdgeDomain;
+
+public class DefaultDomainPermits {
+
+    public static int defaultPermits(EdgeDomain domain) {
+        return defaultPermits(domain.topDomain.toLowerCase());
+    }
+
+    public static int defaultPermits(String topDomain) {
+
+        if (topDomain.equals("wordpress.com"))
+            return 16;
+        if (topDomain.equals("blogspot.com"))
+            return 8;
+        if (topDomain.equals("tumblr.com"))
+            return 8;
+        if (topDomain.equals("neocities.org"))
+            return 8;
+        if (topDomain.equals("github.io"))
+            return 8;
+        // Substack really dislikes broad-scale crawlers, so we need to be careful
+        // to not get blocked.
+        if (topDomain.equals("substack.com")) {
+            return 1;
+        }
+
+        return 2;
+    }
+
+}

code/libraries/domain-lock/java/nu/marginalia/coordination/DomainCoordinationModule.java

@@ -0,0 +1,17 @@
+package nu.marginalia.coordination;
+
+import com.google.inject.AbstractModule;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class DomainCoordinationModule extends AbstractModule {
+
+    private static final Logger logger = LoggerFactory.getLogger(DomainCoordinationModule.class);
+
+    public DomainCoordinationModule() {
+    }
+
+    public void configure() {
+        bind(DomainCoordinator.class).to(ZookeeperDomainCoordinator.class);
+    }
+}

code/libraries/domain-lock/java/nu/marginalia/coordination/DomainCoordinator.java

@@ -0,0 +1,13 @@
+package nu.marginalia.coordination;
+
+import nu.marginalia.model.EdgeDomain;
+
+import java.time.Duration;
+import java.util.Optional;
+
+public interface DomainCoordinator {
+    DomainLock lockDomain(EdgeDomain domain) throws InterruptedException;
+    Optional<DomainLock> tryLockDomain(EdgeDomain domain, Duration timeout) throws InterruptedException;
+    Optional<DomainLock> tryLockDomain(EdgeDomain domain)  throws InterruptedException;
+    boolean isLockableHint(EdgeDomain domain);
+}

code/libraries/domain-lock/java/nu/marginalia/coordination/DomainLock.java

@@ -0,0 +1,5 @@
+package nu.marginalia.coordination;
+
+public interface DomainLock extends AutoCloseable {
+    void close();
+}

code/libraries/domain-lock/java/nu/marginalia/coordination/LocalDomainCoordinator.java

@@ -1,16 +1,15 @@
-package nu.marginalia.crawl.logic;
+package nu.marginalia.coordination;
 
 import nu.marginalia.model.EdgeDomain;
 
+import java.time.Duration;
 import java.util.Map;
 import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.Semaphore;
+import java.util.concurrent.TimeUnit;
 
-/** Holds lock objects for each domain, to prevent multiple threads from
+public class LocalDomainCoordinator implements DomainCoordinator {
- * crawling the same domain at the same time.
- */
-public class DomainLocks {
     // The locks are stored in a map, with the domain name as the key.  This map will grow
     // relatively big, but should be manageable since the number of domains is limited to
     // a few hundred thousand typically.
@@ -24,13 +23,25 @@ public class DomainLocks {
 
         sem.acquire();
 
-        return new DomainLock(sem);
+        return new LocalDomainLock(sem);
     }
 
     public Optional<DomainLock> tryLockDomain(EdgeDomain domain) {
         var sem = locks.computeIfAbsent(domain.topDomain.toLowerCase(), this::defaultPermits);
         if (sem.tryAcquire(1)) {
-            return Optional.of(new DomainLock(sem));
+            return Optional.of(new LocalDomainLock(sem));
+        }
+        else {
+            // We don't have a lock, so we return an empty optional
+            return Optional.empty();
+        }
+    }
+
+
+    public Optional<DomainLock> tryLockDomain(EdgeDomain domain, Duration timeout) throws InterruptedException {
+        var sem = locks.computeIfAbsent(domain.topDomain.toLowerCase(), this::defaultPermits);
+        if (sem.tryAcquire(1, timeout.toMillis(), TimeUnit.MILLISECONDS)) {
+            return Optional.of(new LocalDomainLock(sem));
         }
         else {
             // We don't have a lock, so we return an empty optional
@@ -39,24 +50,7 @@ public class DomainLocks {
     }
 
     private Semaphore defaultPermits(String topDomain) {
-        if (topDomain.equals("wordpress.com"))
+        return new Semaphore(DefaultDomainPermits.defaultPermits(topDomain));
-            return new Semaphore(16);
-        if (topDomain.equals("blogspot.com"))
-            return new Semaphore(8);
-        if (topDomain.equals("tumblr.com"))
-            return new Semaphore(8);
-        if (topDomain.equals("neocities.org"))
-            return new Semaphore(8);
-        if (topDomain.equals("github.io"))
-            return new Semaphore(8);
-
-        // Substack really dislikes broad-scale crawlers, so we need to be careful
-        // to not get blocked.
-        if (topDomain.equals("substack.com")) {
-            return new Semaphore(1);
-        }
-
-        return new Semaphore(2);
     }
 
     /** Returns true if the domain is lockable, i.e. if it is not already locked by another thread.
@@ -71,15 +65,15 @@ public class DomainLocks {
             return sem.availablePermits() > 0;
     }
 
-    public static class DomainLock implements AutoCloseable {
+    public static class LocalDomainLock implements DomainLock {
         private final Semaphore semaphore;
 
-        DomainLock(Semaphore semaphore) {
+        LocalDomainLock(Semaphore semaphore) {
             this.semaphore = semaphore;
         }
 
         @Override
-        public void close() throws Exception {
+        public void close() {
             semaphore.release();
             Thread.currentThread().setName("[idle]");
         }

code/libraries/domain-lock/java/nu/marginalia/coordination/ZookeeperDomainCoordinator.java

@@ -0,0 +1,101 @@
+package nu.marginalia.coordination;
+
+import com.google.inject.Inject;
+import com.google.inject.name.Named;
+import nu.marginalia.model.EdgeDomain;
+import nu.marginalia.service.discovery.ServiceRegistryIf;
+import org.apache.curator.framework.recipes.locks.InterProcessSemaphoreV2;
+import org.apache.curator.framework.recipes.locks.Lease;
+
+import java.time.Duration;
+import java.util.Map;
+import java.util.Optional;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.TimeUnit;
+
+public class ZookeeperDomainCoordinator implements DomainCoordinator {
+    // The locks are stored in a map, with the domain name as the key.  This map will grow
+    // relatively big, but should be manageable since the number of domains is limited to
+    // a few hundred thousand typically.
+    private final Map<String, InterProcessSemaphoreV2> locks = new ConcurrentHashMap<>();
+    private final ServiceRegistryIf serviceRegistry;
+    private final int nodeId;
+
+    @Inject
+    public ZookeeperDomainCoordinator(ServiceRegistryIf serviceRegistry, @Named("wmsa-system-node") int nodeId) {
+        // Zookeeper-specific initialization can be done here if needed
+        this.serviceRegistry = serviceRegistry;
+        this.nodeId = nodeId;
+    }
+
+    /** Returns a lock object corresponding to the given domain.  The object is returned as-is,
+     * and may be held by another thread.  The caller is responsible for locking and  releasing the lock.
+     */
+    public DomainLock lockDomain(EdgeDomain domain) throws InterruptedException {
+        var sem = locks.computeIfAbsent(domain.topDomain.toLowerCase(), this::createSemapore);
+
+        try {
+            var lease = sem.acquire();
+
+            return new ZkDomainLock(sem, lease);
+        }
+        catch (Exception e) {
+            throw new RuntimeException("Failed to acquire lock for domain: " + domain.topDomain, e);
+        }
+    }
+
+    public Optional<DomainLock> tryLockDomain(EdgeDomain domain) throws InterruptedException {
+        return tryLockDomain(domain, Duration.ofSeconds(1)); // Underlying semaphore doesn't have a tryLock method, so we use a short timeout
+    }
+
+
+    public Optional<DomainLock> tryLockDomain(EdgeDomain domain, Duration timeout) throws InterruptedException {
+
+        var sem = locks.computeIfAbsent(domain.topDomain.toLowerCase(), this::createSemapore);
+
+        try {
+            var lease = sem.acquire(timeout.toMillis(), TimeUnit.MILLISECONDS); // Acquire with timeout
+            if (lease != null) {
+                return Optional.of(new ZkDomainLock(sem, lease));
+            }
+            else {
+                return Optional.empty(); // If we fail to acquire the lease, we return an empty optional
+            }
+        }
+        catch (Exception e) {
+            return Optional.empty(); // If we fail to acquire the lock, we return an empty optional
+        }
+    }
+
+    private InterProcessSemaphoreV2 createSemapore(String topDomain){
+        try {
+            return serviceRegistry.getSemaphore(topDomain + ":" + nodeId, DefaultDomainPermits.defaultPermits(topDomain));
+        }
+        catch (Exception e) {
+            throw new RuntimeException("Failed to get semaphore for domain: " + topDomain, e);
+        }
+    }
+
+    /** Returns true if the domain is lockable, i.e. if it is not already locked by another thread.
+     * (this is just a hint, and does not guarantee that the domain is actually lockable any time
+     * after this method returns true)
+     */
+    public boolean isLockableHint(EdgeDomain domain) {
+        return true; // Curator does not provide a way to check if a lock is available without acquiring it
+    }
+
+    public static class ZkDomainLock implements DomainLock {
+        private final InterProcessSemaphoreV2 semaphore;
+        private final Lease lease;
+
+        ZkDomainLock(InterProcessSemaphoreV2 semaphore, Lease lease) {
+            this.semaphore = semaphore;
+            this.lease = lease;
+        }
+
+        @Override
+        public void close() {
+            semaphore.returnLease(lease);
+        }
+    }
+}

code/processes/crawling-process/build.gradle

@@ -32,6 +32,7 @@ dependencies {
     implementation project(':code:libraries:message-queue')
     implementation project(':code:libraries:language-processing')
     implementation project(':code:libraries:easy-lsh')
+    implementation project(':code:libraries:domain-lock')
     implementation project(':code:processes:crawling-process:model')
     implementation project(':code:processes:crawling-process:model')
 

code/processes/crawling-process/java/nu/marginalia/crawl/CrawlerMain.java

@@ -10,9 +10,11 @@ import nu.marginalia.WmsaHome;
 import nu.marginalia.atags.model.DomainLinks;
 import nu.marginalia.atags.source.AnchorTagsSource;
 import nu.marginalia.atags.source.AnchorTagsSourceFactory;
+import nu.marginalia.coordination.DomainCoordinationModule;
+import nu.marginalia.coordination.DomainCoordinator;
+import nu.marginalia.coordination.DomainLock;
 import nu.marginalia.crawl.fetcher.HttpFetcherImpl;
 import nu.marginalia.crawl.fetcher.warc.WarcRecorder;
-import nu.marginalia.crawl.logic.DomainLocks;
 import nu.marginalia.crawl.retreival.CrawlDataReference;
 import nu.marginalia.crawl.retreival.CrawlerRetreiver;
 import nu.marginalia.crawl.retreival.DomainProber;
@@ -68,7 +70,7 @@ public class CrawlerMain extends ProcessMainClass {
     private final ServiceRegistryIf serviceRegistry;
     private final SimpleBlockingThreadPool pool;
 
-    private final DomainLocks domainLocks = new DomainLocks();
+    private final DomainCoordinator domainCoordinator;
 
     private final Map<String, CrawlTask> pendingCrawlTasks = new ConcurrentHashMap<>();
 
@@ -97,6 +99,7 @@ public class CrawlerMain extends ProcessMainClass {
                        WarcArchiverFactory warcArchiverFactory,
                        HikariDataSource dataSource,
                        DomainBlacklist blacklist,
+                       DomainCoordinator domainCoordinator,
                        ServiceRegistryIf serviceRegistry,
                        Gson gson) throws InterruptedException {
 
@@ -114,6 +117,7 @@ public class CrawlerMain extends ProcessMainClass {
         this.blacklist = blacklist;
         this.node = processConfiguration.node();
         this.serviceRegistry = serviceRegistry;
+        this.domainCoordinator = domainCoordinator;
 
         SimpleBlockingThreadPool.ThreadType threadType;
         if (Boolean.getBoolean("crawler.useVirtualThreads")) {
@@ -157,6 +161,7 @@ public class CrawlerMain extends ProcessMainClass {
                     new CrawlerModule(),
                     new ProcessConfigurationModule("crawler"),
                     new ServiceDiscoveryModule(),
+                    new DomainCoordinationModule(),
                     new DatabaseModule(false)
             );
             var crawler = injector.getInstance(CrawlerMain.class);
@@ -451,7 +456,7 @@ public class CrawlerMain extends ProcessMainClass {
         /** Best effort indicator whether we could start this now without getting stuck in
          * DomainLocks purgatory */
         public boolean canRun() {
-            return domainLocks.isLockableHint(new EdgeDomain(domain));
+            return domainCoordinator.isLockableHint(new EdgeDomain(domain));
         }
 
         @Override
@@ -462,7 +467,7 @@ public class CrawlerMain extends ProcessMainClass {
                 return;
             }
 
-            Optional<DomainLocks.DomainLock> lock = domainLocks.tryLockDomain(new EdgeDomain(domain));
+            Optional<DomainLock> lock = domainCoordinator.tryLockDomain(new EdgeDomain(domain));
             // We don't have a lock, so we can't run this task
             // we return to avoid blocking the pool for too long
             if (lock.isEmpty()) {
@@ -470,7 +475,7 @@ public class CrawlerMain extends ProcessMainClass {
                 retryQueue.put(this);
                 return;
             }
-            DomainLocks.DomainLock domainLock = lock.get();
+            DomainLock domainLock = lock.get();
 
             try (domainLock) {
                 Thread.currentThread().setName("crawling:" + domain);

code/processes/live-crawling-process/build.gradle

@@ -32,6 +32,7 @@ dependencies {
     implementation project(':code:index:api')
     implementation project(':code:processes:process-mq-api')
     implementation project(':code:libraries:message-queue')
+    implementation project(':code:libraries:domain-lock')
     implementation project(':code:libraries:language-processing')
     implementation project(':code:libraries:easy-lsh')
     implementation project(':code:processes:crawling-process')

code/processes/live-crawling-process/java/nu/marginalia/livecrawler/LiveCrawlerMain.java

@@ -10,6 +10,8 @@ import nu.marginalia.api.feeds.FeedsClient;
 import nu.marginalia.converting.ConverterModule;
 import nu.marginalia.converting.processor.DomainProcessor;
 import nu.marginalia.converting.writer.ConverterBatchWriter;
+import nu.marginalia.coordination.DomainCoordinationModule;
+import nu.marginalia.coordination.DomainCoordinator;
 import nu.marginalia.db.DbDomainQueries;
 import nu.marginalia.db.DomainBlacklist;
 import nu.marginalia.io.SerializableCrawlDataStream;
@@ -58,6 +60,7 @@ public class LiveCrawlerMain extends ProcessMainClass {
     private final FileStorageService fileStorageService;
     private final KeywordLoaderService keywordLoaderService;
     private final DocumentLoaderService documentLoaderService;
+    private final DomainCoordinator domainCoordinator;
     private final HikariDataSource dataSource;
 
     @Inject
@@ -71,7 +74,7 @@ public class LiveCrawlerMain extends ProcessMainClass {
                            DomainProcessor domainProcessor,
                            FileStorageService fileStorageService,
                            KeywordLoaderService keywordLoaderService,
-                           DocumentLoaderService documentLoaderService, HikariDataSource dataSource)
+                           DocumentLoaderService documentLoaderService, DomainCoordinator domainCoordinator, HikariDataSource dataSource)
             throws Exception
     {
         super(messageQueueFactory, config, gson, LIVE_CRAWLER_INBOX);
@@ -84,6 +87,7 @@ public class LiveCrawlerMain extends ProcessMainClass {
         this.fileStorageService = fileStorageService;
         this.keywordLoaderService = keywordLoaderService;
         this.documentLoaderService = documentLoaderService;
+        this.domainCoordinator = domainCoordinator;
         this.dataSource = dataSource;
 
         domainBlacklist.waitUntilLoaded();
@@ -107,6 +111,7 @@ public class LiveCrawlerMain extends ProcessMainClass {
         try {
             Injector injector = Guice.createInjector(
                     new LiveCrawlerModule(),
+                    new DomainCoordinationModule(), // 2 hours lease timeout is enough for the live crawler
                     new ProcessConfigurationModule("crawler"),
                     new ConverterModule(),
                     new ServiceDiscoveryModule(),
@@ -172,7 +177,7 @@ public class LiveCrawlerMain extends ProcessMainClass {
 
             processHeartbeat.progress(LiveCrawlState.CRAWLING);
 
-            try (SimpleLinkScraper fetcher = new SimpleLinkScraper(dataSet, domainQueries, domainBlacklist);
+            try (SimpleLinkScraper fetcher = new SimpleLinkScraper(dataSet, domainCoordinator, domainQueries, domainBlacklist);
                  var hb = heartbeat.createAdHocTaskHeartbeat("Live Crawling"))
             {
                 for (Map.Entry<String, List<String>> entry : hb.wrap("Fetching", urlsPerDomain.entrySet())) {

code/processes/live-crawling-process/java/nu/marginalia/livecrawler/SimpleLinkScraper.java

@@ -5,8 +5,9 @@ import crawlercommons.robots.SimpleRobotRulesParser;
 import nu.marginalia.WmsaHome;
 import nu.marginalia.contenttype.ContentType;
 import nu.marginalia.contenttype.DocumentBodyToString;
+import nu.marginalia.coordination.DomainCoordinator;
+import nu.marginalia.coordination.DomainLock;
 import nu.marginalia.crawl.fetcher.HttpFetcherImpl;
-import nu.marginalia.crawl.logic.DomainLocks;
 import nu.marginalia.crawl.retreival.CrawlDelayTimer;
 import nu.marginalia.db.DbDomainQueries;
 import nu.marginalia.db.DomainBlacklist;
@@ -46,14 +47,16 @@ public class SimpleLinkScraper implements AutoCloseable {
     private final DomainBlacklist domainBlacklist;
     private final Duration connectTimeout = Duration.ofSeconds(10);
     private final Duration readTimeout = Duration.ofSeconds(10);
-    private final DomainLocks domainLocks = new DomainLocks();
+    private final DomainCoordinator domainCoordinator;
 
     private final static int MAX_SIZE = Integer.getInteger("crawler.maxFetchSize", 10 * 1024 * 1024);
 
     public SimpleLinkScraper(LiveCrawlDataSet dataSet,
+                             DomainCoordinator domainCoordinator,
                              DbDomainQueries domainQueries,
                              DomainBlacklist domainBlacklist) {
         this.dataSet = dataSet;
+        this.domainCoordinator = domainCoordinator;
         this.domainQueries = domainQueries;
         this.domainBlacklist = domainBlacklist;
     }
@@ -98,7 +101,7 @@ public class SimpleLinkScraper implements AutoCloseable {
                 .version(HttpClient.Version.HTTP_2)
                 .build();
              // throttle concurrent access per domain; IDE will complain it's not used, but it holds a semaphore -- do not remove:
-             DomainLocks.DomainLock lock = domainLocks.lockDomain(domain)
+             DomainLock lock = domainCoordinator.lockDomain(domain)
         ) {
             SimpleRobotRules rules = fetchRobotsRules(rootUrl, client);
 

code/processes/live-crawling-process/test/nu/marginalia/livecrawler/SimpleLinkScraperTest.java

@@ -1,5 +1,6 @@
 package nu.marginalia.livecrawler;
 
+import nu.marginalia.coordination.LocalDomainCoordinator;
 import nu.marginalia.db.DomainBlacklistImpl;
 import nu.marginalia.io.SerializableCrawlDataStream;
 import nu.marginalia.model.EdgeDomain;
@@ -37,7 +38,7 @@ class SimpleLinkScraperTest {
 
     @Test
     public void testRetrieveNow() throws Exception {
-        var scraper = new SimpleLinkScraper(dataSet, null, Mockito.mock(DomainBlacklistImpl.class));
+        var scraper = new SimpleLinkScraper(dataSet, new LocalDomainCoordinator(),  null, Mockito.mock(DomainBlacklistImpl.class));
         int fetched = scraper.retrieveNow(new EdgeDomain("www.marginalia.nu"), 1, List.of("https://www.marginalia.nu/"));
         Assertions.assertEquals(1, fetched);
 
@@ -57,7 +58,7 @@ class SimpleLinkScraperTest {
     @Test
     public void testRetrieveNow_Redundant() throws Exception {
         dataSet.saveDocument(1, new EdgeUrl("https://www.marginalia.nu/"), "<html>", "", "127.0.0.1");
-        var scraper = new SimpleLinkScraper(dataSet, null, Mockito.mock(DomainBlacklistImpl.class));
+        var scraper = new SimpleLinkScraper(dataSet, new LocalDomainCoordinator(),null, Mockito.mock(DomainBlacklistImpl.class));
 
         // If the requested URL is already in the dataSet, we retrieveNow should shortcircuit and not fetch anything
         int fetched = scraper.retrieveNow(new EdgeDomain("www.marginalia.nu"), 1, List.of("https://www.marginalia.nu/"));

code/processes/ping-process/build.gradle

@@ -27,6 +27,7 @@ dependencies {
     implementation project(':code:common:config')
     implementation project(':code:common:service')
 
+    implementation project(':code:libraries:domain-lock')
     implementation project(':code:libraries:geo-ip')
     implementation project(':code:libraries:message-queue')
 

code/processes/ping-process/java/nu/marginalia/ping/PingJobScheduler.java

@@ -1,6 +1,7 @@
 package nu.marginalia.ping;
 
 import com.google.inject.Inject;
+import nu.marginalia.coordination.DomainCoordinator;
 import nu.marginalia.ping.model.*;
 import nu.marginalia.ping.svc.DnsPingService;
 import nu.marginalia.ping.svc.HttpPingService;
@@ -23,6 +24,7 @@ import java.util.concurrent.TimeUnit;
 public class PingJobScheduler {
     private final HttpPingService httpPingService;
     private final DnsPingService dnsPingService;
+    private final DomainCoordinator domainCoordinator;
     private final PingDao pingDao;
 
     private static final Logger logger = LoggerFactory.getLogger(PingJobScheduler.class);
@@ -43,14 +45,16 @@ public class PingJobScheduler {
     @Inject
     public PingJobScheduler(HttpPingService httpPingService,
                             DnsPingService dnsPingService,
+                            DomainCoordinator domainCoordinator,
                             PingDao pingDao)
     {
         this.httpPingService = httpPingService;
         this.dnsPingService = dnsPingService;
+        this.domainCoordinator = domainCoordinator;
         this.pingDao = pingDao;
     }
 
-    public synchronized void start(boolean startPaused) {
+    public synchronized void start() {
         if (running)
             return;
 
@@ -100,7 +104,7 @@ public class PingJobScheduler {
         logger.info("PingJobScheduler paused");
     }
 
-    public synchronized void resume(int nodeId) {
+    public synchronized void enableForNode(int nodeId) {
         logger.info("Resuming PingJobScheduler for nodeId: {}", nodeId);
         if (this.nodeId != null) {
             logger.warn("Attempted to resume PingJobScheduler with mismatched nodeId: expected {}, got {}", this.nodeId, nodeId);

code/processes/ping-process/java/nu/marginalia/ping/PingMain.java

@@ -5,15 +5,14 @@ import com.google.inject.Guice;
 import com.google.inject.Inject;
 import com.google.inject.Injector;
 import nu.marginalia.WmsaHome;
+import nu.marginalia.coordination.DomainCoordinationModule;
 import nu.marginalia.geoip.GeoIpDictionary;
 import nu.marginalia.mq.MessageQueueFactory;
 import nu.marginalia.mqapi.ProcessInboxNames;
 import nu.marginalia.mqapi.ping.PingRequest;
-import nu.marginalia.nodecfg.NodeConfigurationService;
 import nu.marginalia.process.ProcessConfiguration;
 import nu.marginalia.process.ProcessConfigurationModule;
 import nu.marginalia.process.ProcessMainClass;
-import nu.marginalia.service.discovery.ServiceRegistryIf;
 import nu.marginalia.service.module.DatabaseModule;
 import nu.marginalia.service.module.ServiceDiscoveryModule;
 import org.slf4j.Logger;
@@ -25,8 +24,6 @@ public class PingMain extends ProcessMainClass {
     private static final Logger log = LoggerFactory.getLogger(PingMain.class);
 
     private final PingJobScheduler pingJobScheduler;
-    private final ServiceRegistryIf serviceRegistry;
-    private final NodeConfigurationService nodeConfigurationService;
     private final int node;
 
     private static final Logger logger = LoggerFactory.getLogger(PingMain.class);
@@ -36,15 +33,11 @@ public class PingMain extends ProcessMainClass {
                     ProcessConfiguration config,
                     Gson gson,
                     PingJobScheduler pingJobScheduler,
-                    ServiceRegistryIf serviceRegistry,
-                    NodeConfigurationService nodeConfigurationService,
                     ProcessConfiguration processConfiguration
                     ) {
         super(messageQueueFactory, config, gson, ProcessInboxNames.PING_INBOX);
 
         this.pingJobScheduler = pingJobScheduler;
-        this.serviceRegistry = serviceRegistry;
-        this.nodeConfigurationService = nodeConfigurationService;
         this.node = processConfiguration.node();
     }
 
@@ -52,7 +45,8 @@ public class PingMain extends ProcessMainClass {
         log.info("Starting PingMain...");
 
         // Start the ping job scheduler
-        pingJobScheduler.start(true);
+        pingJobScheduler.start();
+        pingJobScheduler.enableForNode(node);
 
         log.info("PingMain started successfully.");
     }
@@ -79,6 +73,7 @@ public class PingMain extends ProcessMainClass {
         Injector injector = Guice.createInjector(
                 new PingModule(),
                 new ServiceDiscoveryModule(),
+                new DomainCoordinationModule(),
                 new ProcessConfigurationModule("ping"),
                 new DatabaseModule(false)
         );

code/processes/ping-process/java/nu/marginalia/ping/io/RetryStrategy.java

@@ -50,7 +50,12 @@ public class RetryStrategy implements HttpRequestRetryStrategy {
 
         if (statusCode == 429) {
             // get the Retry-After header
-            String retryAfter = response.getFirstHeader("Retry-After").getValue();
+            var retryAfterHeader = response.getFirstHeader("Retry-After");
+            if (retryAfterHeader == null) {
+                return TimeValue.ofSeconds(3);
+            }
+
+            String retryAfter = retryAfterHeader.getValue();
             if (retryAfter == null) {
                 return TimeValue.ofSeconds(2);
             }

code/processes/ping-process/java/nu/marginalia/ping/model/DomainReference.java

@@ -1,3 +1,10 @@
 package nu.marginalia.ping.model;
 
-public record DomainReference(int domainId, int nodeId, String domainName) { }
+import nu.marginalia.model.EdgeDomain;
+
+public record DomainReference(int domainId, int nodeId, String domainName) {
+    public EdgeDomain asEdgeDomain() {
+        return new EdgeDomain(domainName);
+    }
+
+}

code/processes/ping-process/java/nu/marginalia/ping/svc/HttpPingService.java

@@ -2,6 +2,7 @@ package nu.marginalia.ping.svc;
 
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
+import nu.marginalia.coordination.DomainCoordinator;
 import nu.marginalia.ping.fetcher.PingHttpFetcher;
 import nu.marginalia.ping.fetcher.response.*;
 import nu.marginalia.ping.model.*;
@@ -26,6 +27,7 @@ import java.util.List;
 @Singleton
 public class HttpPingService {
 
+    private final DomainCoordinator domainCoordinator;
     private final PingHttpFetcher pingHttpFetcher;
 
     private final DomainAvailabilityInformationFactory domainAvailabilityInformationFactory;
@@ -36,9 +38,11 @@ public class HttpPingService {
 
     @Inject
     public HttpPingService(
+            DomainCoordinator domainCoordinator,
             PingHttpFetcher pingHttpFetcher,
             DomainAvailabilityInformationFactory domainAvailabilityInformationFactory,
             DomainSecurityInformationFactory domainSecurityInformationFactory) throws Exception {
+        this.domainCoordinator = domainCoordinator;
         this.pingHttpFetcher = pingHttpFetcher;
         this.domainAvailabilityInformationFactory = domainAvailabilityInformationFactory;
         this.domainSecurityInformationFactory = domainSecurityInformationFactory;
@@ -59,7 +63,8 @@ public class HttpPingService {
 
     public List<WritableModel> pingDomain(DomainReference domainReference,
                            @Nullable DomainAvailabilityRecord oldPingStatus,
-                           @Nullable DomainSecurityRecord oldSecurityInformation) throws SQLException {
+                           @Nullable DomainSecurityRecord oldSecurityInformation) throws SQLException, InterruptedException {
+
         // First we figure out if the domain maps to an IP address
 
         List<WritableModel> generatedRecords = new ArrayList<>();
@@ -69,26 +74,31 @@ public class HttpPingService {
 
         if (ipAddress.isEmpty()) {
             result = new UnknownHostError();
-        }
+        } else {
-        else {
+            // lock the domain to prevent concurrent pings
-            String url = "https://" + domainReference.domainName() + "/";
+            try (var _ = domainCoordinator.lockDomain(domainReference.asEdgeDomain())) {
-            String alternateUrl = "http://" + domainReference.domainName() + "/";
+                String url = "https://" + domainReference.domainName() + "/";
+                String alternateUrl = "http://" + domainReference.domainName() + "/";
 
-            result = pingHttpFetcher.fetchUrl(url, Method.HEAD, null, null);
+                result = pingHttpFetcher.fetchUrl(url, Method.HEAD, null, null);
 
-            if (result instanceof HttpsResponse response && shouldTryGET(response.httpStatus())) {
+                if (result instanceof HttpsResponse response && shouldTryGET(response.httpStatus())) {
-                sleep(Duration.ofSeconds(2));
-                result = pingHttpFetcher.fetchUrl(url, Method.GET, null, null);
-            }
-            else if (result instanceof ConnectionError) {
-                var result2 = pingHttpFetcher.fetchUrl(alternateUrl, Method.HEAD, null, null);
-                if (!(result2 instanceof ConnectionError)) {
-                    result = result2;
-                }
-                if (result instanceof HttpResponse response && shouldTryGET(response.httpStatus())) {
                     sleep(Duration.ofSeconds(2));
-                    result = pingHttpFetcher.fetchUrl(alternateUrl, Method.GET, null, null);
+                    result = pingHttpFetcher.fetchUrl(url, Method.GET, null, null);
+                } else if (result instanceof ConnectionError) {
+                    var result2 = pingHttpFetcher.fetchUrl(alternateUrl, Method.HEAD, null, null);
+                    if (!(result2 instanceof ConnectionError)) {
+                        result = result2;
+                    }
+                    if (result instanceof HttpResponse response && shouldTryGET(response.httpStatus())) {
+                        sleep(Duration.ofSeconds(2));
+                        result = pingHttpFetcher.fetchUrl(alternateUrl, Method.GET, null, null);
+                    }
                 }
+
+                // Add a grace sleep before we yield the semaphore, so that another thread doesn't
+                // immediately hammer the same domain after it's released.
+                sleep(Duration.ofSeconds(1));
             }
         }
 
@@ -186,8 +196,8 @@ public class HttpPingService {
         }
         if (oldSecurityInformation != null && newSecurityInformation != null) {
             compareSecurityInformation(generatedRecords,
-                                       oldSecurityInformation, oldPingStatus,
+                    oldSecurityInformation, oldPingStatus,
-                                       newSecurityInformation, newPingStatus);
+                    newSecurityInformation, newPingStatus);
         }
 
         return generatedRecords;

code/processes/ping-process/test/nu/marginalia/ping/AvailabilityJobSchedulerTest.java

@@ -2,6 +2,7 @@ package nu.marginalia.ping;
 
 import com.zaxxer.hikari.HikariConfig;
 import com.zaxxer.hikari.HikariDataSource;
+import nu.marginalia.coordination.LocalDomainCoordinator;
 import nu.marginalia.geoip.GeoIpDictionary;
 import nu.marginalia.ping.fetcher.PingDnsFetcher;
 import nu.marginalia.ping.fetcher.PingHttpFetcher;
@@ -90,6 +91,7 @@ class AvailabilityJobSchedulerTest {
                         new DomainSecurityInformationFactory()),
                 new DnsPingService(new PingDnsFetcher(List.of("8.8.8.8", "8.8.4.4")),
                         dnsDomainInformationFactory),
+                new LocalDomainCoordinator(),
                 pingDao
         );
 

code/services-core/assistant-service/build.gradle

@@ -37,6 +37,7 @@ dependencies {
     implementation project(':code:functions:domain-info')
     implementation project(':code:functions:domain-info:api')
 
+    implementation project(':code:libraries:domain-lock')
     implementation project(':code:libraries:geo-ip')
     implementation project(':code:libraries:language-processing')
     implementation project(':code:libraries:term-frequency-dict')

code/services-core/assistant-service/java/nu/marginalia/assistant/AssistantMain.java

@@ -5,6 +5,7 @@ import com.google.inject.Inject;
 import com.google.inject.Injector;
 import io.jooby.ExecutionMode;
 import io.jooby.Jooby;
+import nu.marginalia.coordination.DomainCoordinationModule;
 import nu.marginalia.livecapture.LivecaptureModule;
 import nu.marginalia.service.MainClass;
 import nu.marginalia.service.ServiceId;
@@ -29,6 +30,7 @@ public class AssistantMain extends MainClass {
         Injector injector = Guice.createInjector(
                 new AssistantModule(),
                 new LivecaptureModule(),
+                new DomainCoordinationModule(),
                 new ServiceConfigurationModule(ServiceId.Assistant),
                 new ServiceDiscoveryModule(),
                 new DatabaseModule(false)

settings.gradle

@@ -55,6 +55,7 @@ include 'code:libraries:braille-block-punch-cards'
 include 'code:libraries:language-processing'
 include 'code:libraries:term-frequency-dict'
 include 'code:libraries:test-helpers'
+include 'code:libraries:domain-lock'
 
 include 'code:libraries:message-queue'