/
LockIterator.java
102 lines (93 loc) · 2.95 KB
/
LockIterator.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
/*
* Copyright 2015 Austin Keener, Michael Ritter, Florian Spieß, and the JDA contributors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package net.dv8tion.jda.api.utils;
import net.dv8tion.jda.api.utils.cache.CacheView;
import net.dv8tion.jda.internal.utils.JDALogger;
import org.slf4j.Logger;
import javax.annotation.Nonnull;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.concurrent.locks.Lock;
/**
* Simple implementation of a {@link ClosableIterator} that uses a lock.
* <br>Close is an idempotent function and can be performed multiple times without effects beyond first invocation.
* <br>This is deployed by {@link CacheView#lockedIterator()} to allow read-only access
* to the underlying structure without the need to clone it, unlike the normal iterator.
*
* <p>This closes automatically when {@link #hasNext()} returns {@code false} but
* its recommended to only be used within a {@code try-with-resources} block for safety.
*
* <h2>Example</h2>
* This can handle any exceptions thrown while iterating and ensures the lock is released correctly.
* <pre>{@code
* try (ClosableIterator<T> it = cacheView.lockedIterator()) {
* while (it.hasNext()) {
* consume(it.next());
* }
* }
* }</pre>
*
* @param <T>
* The element type for this iterator
*
* @since 4.0.0
*/
public class LockIterator<T> implements ClosableIterator<T>
{
private final static Logger log = JDALogger.getLog(ClosableIterator.class);
private final Iterator<? extends T> it;
private Lock lock;
public LockIterator(@Nonnull Iterator<? extends T> it, Lock lock)
{
this.it = it;
this.lock = lock;
}
@Override
public void close()
{
if (lock != null)
lock.unlock();
lock = null;
}
@Override
public boolean hasNext()
{
if (lock == null)
return false;
boolean hasNext = it.hasNext();
if (!hasNext)
close();
return hasNext;
}
@Nonnull
@Override
public T next()
{
if (lock == null)
throw new NoSuchElementException();
return it.next();
}
@Override
@Deprecated //Deprecated in Java 9 because the finalization system is being changed/removed
protected void finalize()
{
if (lock != null)
{
log.error("Finalizing without closing, performing force close on lock");
close();
}
}
}