policy-agent/src/main/java/org/oransc/policyagent/repository/Lock.java

   1 /*-
   2  * ========================LICENSE_START=================================
   3  * O-RAN-SC
   4  * %%
   5  * Copyright (C) 2019 Nordix Foundation
   6  * %%
   7  * Licensed under the Apache License, Version 2.0 (the "License");
   8  * you may not use this file except in compliance with the License.
   9  * You may obtain a copy of the License at
  10  *
  11  *      http://www.apache.org/licenses/LICENSE-2.0
  12  *
  13  * Unless required by applicable law or agreed to in writing, software
  14  * distributed under the License is distributed on an "AS IS" BASIS,
  15  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  16  * See the License for the specific language governing permissions and
  17  * limitations under the License.
  18  * ========================LICENSE_END===================================
  19  */
  20
  21 package org.oransc.policyagent.repository;
  22
  23 import java.util.ArrayList;
  24 import java.util.Iterator;
  25 import java.util.LinkedList;
  26 import java.util.List;
  27
  28 import org.slf4j.Logger;
  29 import org.slf4j.LoggerFactory;
  30
  31 import reactor.core.publisher.Mono;
  32 import reactor.core.publisher.MonoSink;
  33
  34 /**
  35  * A resource lock. Exclusive means that the caller takes exclusive ownership of
  36  * the resurce. Non exclusive lock means that several users can lock the
  37  * resource (for shared usage).
  38  */
  39 public class Lock {
  40     private static final Logger logger = LoggerFactory.getLogger(Lock.class);
  41
  42     private boolean isExclusive = false;
  43     private int lockCounter = 0;
  44     private final List<LockRequest> lockRequestQueue = new LinkedList<>();
  45     private static AsynchCallbackExecutor callbackProcessor = new AsynchCallbackExecutor();
  46
  47     private static class AsynchCallbackExecutor implements Runnable {
  48         private List<LockRequest> lockRequestQueue = new LinkedList<>();
  49
  50         public AsynchCallbackExecutor() {
  51             Thread thread = new Thread(this);
  52             thread.start();
  53         }
  54
  55         public synchronized void addAll(List<LockRequest> requests) {
  56             this.lockRequestQueue.addAll(requests);
  57             this.notifyAll();
  58         }
  59
  60         @Override
  61         public void run() {
  62             try {
  63                 while (true) {
  64                     for (LockRequest request : consume()) {
  65                         request.callback.success(request.lock);
  66                     }
  67                     waitForNewEntries();
  68                 }
  69             } catch (InterruptedException e) {
  70                 Thread.currentThread().interrupt();
  71                 logger.error("Interrupted {}", e.getMessage());
  72             }
  73         }
  74
  75         private synchronized List<LockRequest> consume() {
  76             List<LockRequest> q = this.lockRequestQueue;
  77             this.lockRequestQueue = new LinkedList<>();
  78             return q;
  79         }
  80
  81         @SuppressWarnings("java:S2274")
  82         private synchronized void waitForNewEntries() throws InterruptedException {
  83             if (this.lockRequestQueue.isEmpty()) {
  84                 this.wait();
  85             }
  86         }
  87     }
  88
  89     public enum LockType {
  90         EXCLUSIVE, SHARED
  91     }
  92
  93     /** The caller thread will be blocked util the lock is granted. */
  94     public synchronized void lockBlocking(LockType locktype) {
  95         while (!tryLock(locktype)) {
  96             this.waitForUnlock();
  97         }
  98     }
  99
 100     /** Reactive version. The Lock will be emitted when the lock is granted */
 101     public synchronized Mono<Lock> lock(LockType lockType) {
 102         if (tryLock(lockType)) {
 103             return Mono.just(this);
 104         } else {
 105             return Mono.create(monoSink -> addToQueue(monoSink, lockType));
 106         }
 107     }
 108
 109     public Mono<Lock> unlock() {
 110         return Mono.create(monoSink -> {
 111             unlockBlocking();
 112             monoSink.success(this);
 113         });
 114     }
 115
 116     public void unlockBlocking() {
 117         synchronized (this) {
 118             if (lockCounter <= 0) {
 119                 lockCounter = -1; // Might as well stop, to make it easier to find the problem
 120                 throw new NullPointerException("Number of unlocks must match the number of locks");
 121             }
 122             this.lockCounter--;
 123             if (lockCounter == 0) {
 124                 isExclusive = false;
 125             }
 126             this.notifyAll();
 127         }
 128         this.processQueuedEntries();
 129     }
 130
 131     @Override
 132     public String toString() {
 133         return "Lock cnt: " + this.lockCounter + " exclusive: " + this.isExclusive;
 134     }
 135
 136     /** returns the current number of granted locks */
 137     public synchronized int getLockCounter() {
 138         return this.lockCounter;
 139     }
 140
 141     private void processQueuedEntries() {
 142         List<LockRequest> granted = new ArrayList<>();
 143         synchronized (this) {
 144             for (Iterator<LockRequest> i = lockRequestQueue.iterator(); i.hasNext();) {
 145                 LockRequest request = i.next();
 146                 if (tryLock(request.lockType)) {
 147                     i.remove();
 148                     granted.add(request);
 149                 }
 150             }
 151         }
 152         callbackProcessor.addAll(granted);
 153     }
 154
 155     private static class LockRequest {
 156         final MonoSink<Lock> callback;
 157         final LockType lockType;
 158         final Lock lock;
 159
 160         LockRequest(MonoSink<Lock> callback, LockType lockType, Lock lock) {
 161             this.callback = callback;
 162             this.lockType = lockType;
 163             this.lock = lock;
 164         }
 165     }
 166
 167     private synchronized void addToQueue(MonoSink<Lock> callback, LockType lockType) {
 168         lockRequestQueue.add(new LockRequest(callback, lockType, this));
 169     }
 170
 171     @SuppressWarnings("java:S2274") // Always invoke wait() and await() methods inside a loop
 172     private synchronized void waitForUnlock() {
 173         try {
 174             this.wait();
 175         } catch (InterruptedException e) {
 176             logger.warn("waitForUnlock interrupted", e);
 177             Thread.currentThread().interrupt();
 178         }
 179     }
 180
 181     private boolean tryLock(LockType lockType) {
 182         if (this.isExclusive) {
 183             return false;
 184         }
 185         if (lockType == LockType.EXCLUSIVE && lockCounter > 0) {
 186             return false;
 187         }
 188         lockCounter++;
 189         this.isExclusive = lockType == LockType.EXCLUSIVE;
 190         return true;
 191     }
 192
 193 }