From d4bc97b666203bdd25ccc63e7870526f190cefd5 Mon Sep 17 00:00:00 2001
From: Timm Fitschen <t.fitschen@indiscale.com>
Date: Thu, 4 Mar 2021 23:07:02 +0100
Subject: [PATCH] fix deadlock
---
.../database/DatabaseAccessManager.java | 10 +--
.../database/DatabaseAccessManagerTest.java | 83 +++++++++++++++++++
.../org/caosdb/server/query/QueryTest.java | 4 +-
3 files changed, 89 insertions(+), 8 deletions(-)
diff --git a/src/main/java/org/caosdb/server/database/DatabaseAccessManager.java b/src/main/java/org/caosdb/server/database/DatabaseAccessManager.java
index 196a9fb2..f12c78e3 100644
--- a/src/main/java/org/caosdb/server/database/DatabaseAccessManager.java
+++ b/src/main/java/org/caosdb/server/database/DatabaseAccessManager.java
@@ -26,6 +26,7 @@
package org.caosdb.server.database;
import java.util.concurrent.Semaphore;
+import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantLock;
import org.caosdb.server.database.access.Access;
import org.caosdb.server.database.access.AccessControlAccess;
@@ -56,7 +57,7 @@ import org.caosdb.server.utils.Releasable;
class ReadAccessSemaphore extends Semaphore implements Releasable {
private static final long serialVersionUID = 4384921156838881337L;
- private int acquired = 0; // how many threads have read access
+ private AtomicInteger acquired = new AtomicInteger(0); // how many threads have read access
Semaphore writersBlock =
new Semaphore(1, true); // This semaphore is blocked as long as there are any
// unreleased read permits.
@@ -73,10 +74,9 @@ class ReadAccessSemaphore extends Semaphore implements Releasable {
@Override
public void acquire() throws InterruptedException {
super.acquire(); // Protect the next few lines
- if (this.acquired == 0) {
+ if (this.acquired.getAndIncrement() == 0) {
this.writersBlock.acquire();
}
- this.acquired++;
super.release();
}
@@ -87,9 +87,7 @@ class ReadAccessSemaphore extends Semaphore implements Releasable {
*/
@Override
public void release() {
- this.acquired--;
- if (this.acquired <= 0) { // Last permit: release
- this.acquired = 0;
+ if (this.acquired.decrementAndGet() == 0) { // Last permit: release
if (this.writersBlock.availablePermits() <= 0) {
this.writersBlock.release();
}
diff --git a/src/test/java/org/caosdb/server/database/DatabaseAccessManagerTest.java b/src/test/java/org/caosdb/server/database/DatabaseAccessManagerTest.java
index 8e08131f..f03817ff 100644
--- a/src/test/java/org/caosdb/server/database/DatabaseAccessManagerTest.java
+++ b/src/test/java/org/caosdb/server/database/DatabaseAccessManagerTest.java
@@ -22,6 +22,10 @@
*/
package org.caosdb.server.database;
+import static org.junit.Assert.assertFalse;
+
+import java.util.LinkedList;
+import java.util.List;
import org.junit.Assert;
import org.junit.Test;
@@ -29,6 +33,85 @@ public class DatabaseAccessManagerTest {
public static final ReadAccessSemaphore readAccess = new ReadAccessSemaphore();
public static final WriteAccessLock writeAccess = new WriteAccessLock(readAccess);
+ Thread createReadThread(long wait, String name) {
+ return new Thread(
+ new Runnable() {
+
+ @Override
+ public void run() {
+ try {
+ readAccess.acquire();
+ Thread.sleep(wait);
+ } catch (InterruptedException e) {
+ e.printStackTrace();
+ } finally {
+ readAccess.release();
+ }
+ System.out.println(Thread.currentThread().getName() + " terminated");
+ }
+ },
+ name);
+ }
+
+ Thread createWriteThread(long wait, String name) {
+ return new Thread(
+ new Runnable() {
+
+ @Override
+ public void run() {
+ try {
+ writeAccess.reserve();
+ Thread.sleep(wait);
+ writeAccess.lockInterruptibly();
+ Thread.sleep(wait);
+ } catch (InterruptedException e) {
+ e.printStackTrace();
+ } finally {
+ writeAccess.release();
+ }
+ System.out.println(Thread.currentThread().getName() + " terminated");
+ }
+ },
+ name);
+ }
+
+ @Test
+ public void testDeadLock() throws InterruptedException {
+ List<Thread> ts = new LinkedList<>();
+ for (int i = 0; i < 1000; i++) {
+ Thread t1 = createReadThread(1, "Ra" + i);
+ Thread t2 = createReadThread(2, "Rb" + i);
+ Thread t3 = createReadThread(3, "Rc" + i);
+ Thread t5 = createReadThread(5, "Rd" + i);
+ Thread t7 = createReadThread(7, "Re" + i);
+ Thread t11 = createReadThread(11, "Rf" + i);
+ Thread w5 = createWriteThread(2, "W" + i);
+
+ t1.start();
+ t2.start();
+ w5.start();
+ t3.start();
+ t5.start();
+ t7.start();
+ t11.start();
+
+ ts.add(t1);
+ ts.add(t2);
+ ts.add(t3);
+ ts.add(t5);
+ ts.add(t7);
+ ts.add(t11);
+ ts.add(w5);
+ }
+
+ for (Thread t : ts) {
+ t.join();
+ }
+ for (Thread t : ts) {
+ assertFalse(t.isAlive());
+ }
+ }
+
/**
* Two read-, two write-threads. The read-threads request read access, the write-threads request
* write access.<br>
diff --git a/src/test/java/org/caosdb/server/query/QueryTest.java b/src/test/java/org/caosdb/server/query/QueryTest.java
index da652cb3..26e43ec6 100644
--- a/src/test/java/org/caosdb/server/query/QueryTest.java
+++ b/src/test/java/org/caosdb/server/query/QueryTest.java
@@ -70,8 +70,8 @@ public class QueryTest {
/**
* Assure that {@link WriteTransaction#commit()} calls {@link Query#clearCache()}.
*
- * Since currently the cache shall be cleared whenever there is a commit.
- * */
+ * <p>Since currently the cache shall be cleared whenever there is a commit.
+ */
@Test
public void testEtagChangesAfterWrite() {
String old = Query.getETag();
--
GitLab