Concurrent in queue of Linkedlist
multiple threads add elements to the same queue in parallel and other threads consume elements in it.
When I use LinkedList in the example below, the queue will end up with serveral null value in it, and the size is a constant value. No matter how many times the /consumer is requested, the queue still has null value and the size is non-zero.
So I change Linkedlist to ConcurrentLinkedQueue and the problem disappear.It seems a thread-safe problem.
How can queue has null element? why queue.poll() can't poll the null element in queue?
Example：
@RestController
@RequestMapping("/v1")
public class SendController {
public static Queue<String> queue = new ConcurrentLinkedQueue<>();//ok
public static Queue<String> queue = new LinkedList<>();//will have null value in it and can't poll from it
@GetMapping(value = "/produce")
public String pro() {
String s = UUID.randomUUID().toString();
queue.add(s);
return "true";
}
@GetMapping(value = "/consume")
public String con() {
if(queue.size() == 0) {
return null;
}
return queue.poll();
}
java linked-list queue thread-safety
asked Jan 3 at 4:12
teekteek
307215
add a comment |
multiple threads add elements to the same queue in parallel and other threads consume elements in it.
When I use LinkedList in the example below, the queue will end up with serveral null value in it, and the size is a constant value. No matter how many times the /consumer is requested, the queue still has null value and the size is non-zero.
So I change Linkedlist to ConcurrentLinkedQueue and the problem disappear.It seems a thread-safe problem.
How can queue has null element? why queue.poll() can't poll the null element in queue?
Example：
@RestController
@RequestMapping("/v1")
public class SendController {
public static Queue<String> queue = new ConcurrentLinkedQueue<>();//ok
public static Queue<String> queue = new LinkedList<>();//will have null value in it and can't poll from it
@GetMapping(value = "/produce")
public String pro() {
String s = UUID.randomUUID().toString();
queue.add(s);
return "true";
}
@GetMapping(value = "/consume")
public String con() {
if(queue.size() == 0) {
return null;
}
return queue.poll();
}
java linked-list queue thread-safety
asked Jan 3 at 4:12
teekteek
307215
3
Please read How to Ask and provide a Minimal, Complete, and Verifiable example.
– Rafael
Jan 3 at 4:16
add a comment |
multiple threads add elements to the same queue in parallel and other threads consume elements in it.
When I use LinkedList in the example below, the queue will end up with serveral null value in it, and the size is a constant value. No matter how many times the /consumer is requested, the queue still has null value and the size is non-zero.
So I change Linkedlist to ConcurrentLinkedQueue and the problem disappear.It seems a thread-safe problem.
How can queue has null element? why queue.poll() can't poll the null element in queue?
Example：
@RestController
@RequestMapping("/v1")
public class SendController {
public static Queue<String> queue = new ConcurrentLinkedQueue<>();//ok
public static Queue<String> queue = new LinkedList<>();//will have null value in it and can't poll from it
@GetMapping(value = "/produce")
public String pro() {
String s = UUID.randomUUID().toString();
queue.add(s);
return "true";
}
@GetMapping(value = "/consume")
public String con() {
if(queue.size() == 0) {
return null;
}
return queue.poll();
}
java linked-list queue thread-safety
asked Jan 3 at 4:12
teekteek
307215
multiple threads add elements to the same queue in parallel and other threads consume elements in it.
When I use LinkedList in the example below, the queue will end up with serveral null value in it, and the size is a constant value. No matter how many times the /consumer is requested, the queue still has null value and the size is non-zero.
So I change Linkedlist to ConcurrentLinkedQueue and the problem disappear.It seems a thread-safe problem.
How can queue has null element? why queue.poll() can't poll the null element in queue?
Example：
@RestController
@RequestMapping("/v1")
public class SendController {
public static Queue<String> queue = new ConcurrentLinkedQueue<>();//ok
public static Queue<String> queue = new LinkedList<>();//will have null value in it and can't poll from it
@GetMapping(value = "/produce")
public String pro() {
String s = UUID.randomUUID().toString();
queue.add(s);
return "true";
}
@GetMapping(value = "/consume")
public String con() {
if(queue.size() == 0) {
return null;
}
return queue.poll();
}
java linked-list queue thread-safety
java linked-list queue thread-safety
asked Jan 3 at 4:12
teekteek
307215
asked Jan 3 at 4:12
teekteek
307215
edited Jan 3 at 8:07
teek
asked Jan 3 at 4:12
teekteek
307215
asked Jan 3 at 4:12
teekteek
307215
asked Jan 3 at 4:12
teekteek
307215
307215
3
Please read How to Ask and provide a Minimal, Complete, and Verifiable example.
– Rafael
Jan 3 at 4:16
add a comment |
3
Please read How to Ask and provide a Minimal, Complete, and Verifiable example.
– Rafael
Jan 3 at 4:16
3
3
Please read How to Ask and provide a Minimal, Complete, and Verifiable example.
– Rafael
Jan 3 at 4:16
Please read How to Ask and provide a Minimal, Complete, and Verifiable example.
– Rafael
Jan 3 at 4:16
add a comment |
1 Answer
1
active
oldest
votes
Poll method return null if queue is empty and it can poll null element also.Why null elements are coming within the queue it is strange
package test;
import java.util.LinkedList;
public class TestLL {
public static void main(String args) {
// TODO Auto-generated method stub
LinkedList<String> ll = new LinkedList<>();
System.out.println(ll.poll());
System.out.println(ll.size());
String s = "abc";
ll.add(s);
s = null;
ll.add("cde");
ll.add("efg");
System.out.println(ll.size());
String pollStr = ll.poll();
System.out.println("pollStr=" + pollStr);
System.out.println(ll.size());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println();
ll.add(null);
System.out.println(ll.size());
System.out.println(ll.poll());
System.out.println(ll.size());
}
}
edited Jan 3 at 6:24
Farhana
2,67752335
answered Jan 3 at 5:53
vivekdubeyvivekdubey
1516
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Poll method return null if queue is empty and it can poll null element also.Why null elements are coming within the queue it is strange
package test;
import java.util.LinkedList;
public class TestLL {
public static void main(String args) {
// TODO Auto-generated method stub
LinkedList<String> ll = new LinkedList<>();
System.out.println(ll.poll());
System.out.println(ll.size());
String s = "abc";
ll.add(s);
s = null;
ll.add("cde");
ll.add("efg");
System.out.println(ll.size());
String pollStr = ll.poll();
System.out.println("pollStr=" + pollStr);
System.out.println(ll.size());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println();
ll.add(null);
System.out.println(ll.size());
System.out.println(ll.poll());
System.out.println(ll.size());
}
}
edited Jan 3 at 6:24
Farhana
2,67752335
answered Jan 3 at 5:53
vivekdubeyvivekdubey
1516
add a comment |
Poll method return null if queue is empty and it can poll null element also.Why null elements are coming within the queue it is strange
package test;
import java.util.LinkedList;
public class TestLL {
public static void main(String args) {
// TODO Auto-generated method stub
LinkedList<String> ll = new LinkedList<>();
System.out.println(ll.poll());
System.out.println(ll.size());
String s = "abc";
ll.add(s);
s = null;
ll.add("cde");
ll.add("efg");
System.out.println(ll.size());
String pollStr = ll.poll();
System.out.println("pollStr=" + pollStr);
System.out.println(ll.size());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println();
ll.add(null);
System.out.println(ll.size());
System.out.println(ll.poll());
System.out.println(ll.size());
}
}
edited Jan 3 at 6:24
Farhana
2,67752335
answered Jan 3 at 5:53
vivekdubeyvivekdubey
1516
add a comment |
Poll method return null if queue is empty and it can poll null element also.Why null elements are coming within the queue it is strange
package test;
import java.util.LinkedList;
public class TestLL {
public static void main(String args) {
// TODO Auto-generated method stub
LinkedList<String> ll = new LinkedList<>();
System.out.println(ll.poll());
System.out.println(ll.size());
String s = "abc";
ll.add(s);
s = null;
ll.add("cde");
ll.add("efg");
System.out.println(ll.size());
String pollStr = ll.poll();
System.out.println("pollStr=" + pollStr);
System.out.println(ll.size());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println();
ll.add(null);
System.out.println(ll.size());
System.out.println(ll.poll());
System.out.println(ll.size());
}
}
edited Jan 3 at 6:24
Farhana
2,67752335
answered Jan 3 at 5:53
vivekdubeyvivekdubey
1516
Poll method return null if queue is empty and it can poll null element also.Why null elements are coming within the queue it is strange
package test;
import java.util.LinkedList;
public class TestLL {
public static void main(String args) {
// TODO Auto-generated method stub
LinkedList<String> ll = new LinkedList<>();
System.out.println(ll.poll());
System.out.println(ll.size());
String s = "abc";
ll.add(s);
s = null;
ll.add("cde");
ll.add("efg");
System.out.println(ll.size());
String pollStr = ll.poll();
System.out.println("pollStr=" + pollStr);
System.out.println(ll.size());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println(ll.poll());
System.out.println();
ll.add(null);
System.out.println(ll.size());
System.out.println(ll.poll());
System.out.println(ll.size());
}
}
edited Jan 3 at 6:24
Farhana
2,67752335
answered Jan 3 at 5:53
vivekdubeyvivekdubey
1516
edited Jan 3 at 6:24
Farhana
2,67752335
edited Jan 3 at 6:24
Farhana
2,67752335
edited Jan 3 at 6:24
Farhana
2,67752335
2,67752335
answered Jan 3 at 5:53
vivekdubeyvivekdubey
1516
answered Jan 3 at 5:53
vivekdubeyvivekdubey
1516
answered Jan 3 at 5:53
vivekdubeyvivekdubey
1516
1516
add a comment |
add a comment |
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3
Please read How to Ask and provide a Minimal, Complete, and Verifiable example.
– Rafael
Jan 3 at 4:16