why Synchronized method allowing multiple thread to run concurrently?
I have following program in same file. I have synchronized the run() method.
class MyThread2 implements Runnable {
Thread t;
MyThread2(String s) {
t=new Thread(this,s);
t.start();
}
public synchronized void run() {
for (int i=0;i<3;i++) {
System.out.println("Thread name : "+ Thread.currentThread).getName());
try {
t.sleep(1000);
}
catch (InterruptedException e) {
e.getMessage();
}
}
}
}
class TestSync {
public static void main(String args) {
MyThread2 m1=new MyThread2("My Thread 1");
c.fun();
}
}
class c {
static void fun() {
MyThread2 m1=new MyThread2("My Thread 4");
}
}
output is
Thread name : My Thread 1
Thread name : My Thread 4
Thread name : My Thread 4
Thread name : My Thread 1
Thread name : My Thread 1
Thread name : My Thread 4
My question is why is synchronized method allowing both "My Thread 1" and "My Thread 4" thread access concurrently?
java multithreading synchronized
edited Oct 5 '11 at 10:11
Guillaume
17.7k144665
asked Oct 5 '11 at 10:01
user980089user980089
152111
add a comment |
I have following program in same file. I have synchronized the run() method.
class MyThread2 implements Runnable {
Thread t;
MyThread2(String s) {
t=new Thread(this,s);
t.start();
}
public synchronized void run() {
for (int i=0;i<3;i++) {
System.out.println("Thread name : "+ Thread.currentThread).getName());
try {
t.sleep(1000);
}
catch (InterruptedException e) {
e.getMessage();
}
}
}
}
class TestSync {
public static void main(String args) {
MyThread2 m1=new MyThread2("My Thread 1");
c.fun();
}
}
class c {
static void fun() {
MyThread2 m1=new MyThread2("My Thread 4");
}
}
output is
Thread name : My Thread 1
Thread name : My Thread 4
Thread name : My Thread 4
Thread name : My Thread 1
Thread name : My Thread 1
Thread name : My Thread 4
My question is why is synchronized method allowing both "My Thread 1" and "My Thread 4" thread access concurrently?
java multithreading synchronized
edited Oct 5 '11 at 10:11
Guillaume
17.7k144665
asked Oct 5 '11 at 10:01
user980089user980089
152111
2
The code you posted has at least one syntax error, and is really hard to read as is. Make sure you post your actual code and try to format it legibly.
– Mat
Oct 5 '11 at 10:04
The misconception is that you are locking a method, instead you have a method which locks the instance.
– Peter Lawrey
Oct 5 '11 at 10:14
add a comment |
I have following program in same file. I have synchronized the run() method.
class MyThread2 implements Runnable {
Thread t;
MyThread2(String s) {
t=new Thread(this,s);
t.start();
}
public synchronized void run() {
for (int i=0;i<3;i++) {
System.out.println("Thread name : "+ Thread.currentThread).getName());
try {
t.sleep(1000);
}
catch (InterruptedException e) {
e.getMessage();
}
}
}
}
class TestSync {
public static void main(String args) {
MyThread2 m1=new MyThread2("My Thread 1");
c.fun();
}
}
class c {
static void fun() {
MyThread2 m1=new MyThread2("My Thread 4");
}
}
output is
Thread name : My Thread 1
Thread name : My Thread 4
Thread name : My Thread 4
Thread name : My Thread 1
Thread name : My Thread 1
Thread name : My Thread 4
My question is why is synchronized method allowing both "My Thread 1" and "My Thread 4" thread access concurrently?
java multithreading synchronized
edited Oct 5 '11 at 10:11
Guillaume
17.7k144665
asked Oct 5 '11 at 10:01
user980089user980089
152111
I have following program in same file. I have synchronized the run() method.
class MyThread2 implements Runnable {
Thread t;
MyThread2(String s) {
t=new Thread(this,s);
t.start();
}
public synchronized void run() {
for (int i=0;i<3;i++) {
System.out.println("Thread name : "+ Thread.currentThread).getName());
try {
t.sleep(1000);
}
catch (InterruptedException e) {
e.getMessage();
}
}
}
}
class TestSync {
public static void main(String args) {
MyThread2 m1=new MyThread2("My Thread 1");
c.fun();
}
}
class c {
static void fun() {
MyThread2 m1=new MyThread2("My Thread 4");
}
}
output is
Thread name : My Thread 1
Thread name : My Thread 4
Thread name : My Thread 4
Thread name : My Thread 1
Thread name : My Thread 1
Thread name : My Thread 4
My question is why is synchronized method allowing both "My Thread 1" and "My Thread 4" thread access concurrently?
java multithreading synchronized
java multithreading synchronized
edited Oct 5 '11 at 10:11
Guillaume
17.7k144665
asked Oct 5 '11 at 10:01
user980089user980089
152111
edited Oct 5 '11 at 10:11
Guillaume
17.7k144665
asked Oct 5 '11 at 10:01
user980089user980089
152111
edited Oct 5 '11 at 10:11
Guillaume
17.7k144665
edited Oct 5 '11 at 10:11
Guillaume
17.7k144665
edited Oct 5 '11 at 10:11
Guillaume
17.7k144665
17.7k144665
asked Oct 5 '11 at 10:01
user980089user980089
152111
asked Oct 5 '11 at 10:01
user980089user980089
152111
asked Oct 5 '11 at 10:01
user980089user980089
152111
152111
2
The code you posted has at least one syntax error, and is really hard to read as is. Make sure you post your actual code and try to format it legibly.
– Mat
Oct 5 '11 at 10:04
The misconception is that you are locking a method, instead you have a method which locks the instance.
– Peter Lawrey
Oct 5 '11 at 10:14
add a comment |
2
The code you posted has at least one syntax error, and is really hard to read as is. Make sure you post your actual code and try to format it legibly.
– Mat
Oct 5 '11 at 10:04
The misconception is that you are locking a method, instead you have a method which locks the instance.
– Peter Lawrey
Oct 5 '11 at 10:14
2
2
The code you posted has at least one syntax error, and is really hard to read as is. Make sure you post your actual code and try to format it legibly.
– Mat
Oct 5 '11 at 10:04
The code you posted has at least one syntax error, and is really hard to read as is. Make sure you post your actual code and try to format it legibly.
– Mat
Oct 5 '11 at 10:04
The misconception is that you are locking a method, instead you have a method which locks the instance.
– Peter Lawrey
Oct 5 '11 at 10:14
The misconception is that you are locking a method, instead you have a method which locks the instance.
– Peter Lawrey
Oct 5 '11 at 10:14
add a comment |
1 Answer
1
active
oldest
votes
synchronized methods work at the instance level. Each instance of the class gets its own lock. The lock gets acquired every time any synchronized method of the instance is entered. This prevents multiple threads calling synchronized methods on the same instance (note that this also prevents different synchronized methods from getting called on the same instance).
Now, since you have two instances of your class, each instance gets its own lock. There's nothing to prevent the two threads each operating on its own instance concurrently.
If you do want to prevent this, you could have a synchronized(obj) block inside run(), where obj would be some object shared by both instances of your class:
class MyThread2 implements Runnable {
private static final Object lock = new Object();
...
public void run() {
synchronized(lock) {
...
}
}
}
answered Oct 5 '11 at 10:05
NPENPE
354k65753883
Thanks for the answer
– user980089
Oct 6 '11 at 16:19
If we have only one instance of class and multiple threads, is there possible to run somesynchronizedmethods concurrently?
– Sajad
Feb 15 '14 at 22:04
@ssss: Sure:staticvs non-static, usingsynchronizedblocks with different locks etc. If you need further information, please post a new question.
– NPE
Feb 15 '14 at 22:06
add a comment |
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1 Answer
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active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
synchronized methods work at the instance level. Each instance of the class gets its own lock. The lock gets acquired every time any synchronized method of the instance is entered. This prevents multiple threads calling synchronized methods on the same instance (note that this also prevents different synchronized methods from getting called on the same instance).
Now, since you have two instances of your class, each instance gets its own lock. There's nothing to prevent the two threads each operating on its own instance concurrently.
If you do want to prevent this, you could have a synchronized(obj) block inside run(), where obj would be some object shared by both instances of your class:
class MyThread2 implements Runnable {
private static final Object lock = new Object();
...
public void run() {
synchronized(lock) {
...
}
}
}
answered Oct 5 '11 at 10:05
NPENPE
354k65753883
Thanks for the answer
– user980089
Oct 6 '11 at 16:19
If we have only one instance of class and multiple threads, is there possible to run somesynchronizedmethods concurrently?
– Sajad
Feb 15 '14 at 22:04
@ssss: Sure:staticvs non-static, usingsynchronizedblocks with different locks etc. If you need further information, please post a new question.
– NPE
Feb 15 '14 at 22:06
add a comment |
synchronized methods work at the instance level. Each instance of the class gets its own lock. The lock gets acquired every time any synchronized method of the instance is entered. This prevents multiple threads calling synchronized methods on the same instance (note that this also prevents different synchronized methods from getting called on the same instance).
Now, since you have two instances of your class, each instance gets its own lock. There's nothing to prevent the two threads each operating on its own instance concurrently.
If you do want to prevent this, you could have a synchronized(obj) block inside run(), where obj would be some object shared by both instances of your class:
class MyThread2 implements Runnable {
private static final Object lock = new Object();
...
public void run() {
synchronized(lock) {
...
}
}
}
answered Oct 5 '11 at 10:05
NPENPE
354k65753883
Thanks for the answer
– user980089
Oct 6 '11 at 16:19
If we have only one instance of class and multiple threads, is there possible to run somesynchronizedmethods concurrently?
– Sajad
Feb 15 '14 at 22:04
@ssss: Sure:staticvs non-static, usingsynchronizedblocks with different locks etc. If you need further information, please post a new question.
– NPE
Feb 15 '14 at 22:06
add a comment |
synchronized methods work at the instance level. Each instance of the class gets its own lock. The lock gets acquired every time any synchronized method of the instance is entered. This prevents multiple threads calling synchronized methods on the same instance (note that this also prevents different synchronized methods from getting called on the same instance).
Now, since you have two instances of your class, each instance gets its own lock. There's nothing to prevent the two threads each operating on its own instance concurrently.
If you do want to prevent this, you could have a synchronized(obj) block inside run(), where obj would be some object shared by both instances of your class:
class MyThread2 implements Runnable {
private static final Object lock = new Object();
...
public void run() {
synchronized(lock) {
...
}
}
}
answered Oct 5 '11 at 10:05
NPENPE
354k65753883
synchronized methods work at the instance level. Each instance of the class gets its own lock. The lock gets acquired every time any synchronized method of the instance is entered. This prevents multiple threads calling synchronized methods on the same instance (note that this also prevents different synchronized methods from getting called on the same instance).
Now, since you have two instances of your class, each instance gets its own lock. There's nothing to prevent the two threads each operating on its own instance concurrently.
If you do want to prevent this, you could have a synchronized(obj) block inside run(), where obj would be some object shared by both instances of your class:
class MyThread2 implements Runnable {
private static final Object lock = new Object();
...
public void run() {
synchronized(lock) {
...
}
}
}
answered Oct 5 '11 at 10:05
NPENPE
354k65753883
edited Oct 5 '11 at 10:30
answered Oct 5 '11 at 10:05
NPENPE
354k65753883
answered Oct 5 '11 at 10:05
NPENPE
354k65753883
answered Oct 5 '11 at 10:05
NPENPE
354k65753883
354k65753883
Thanks for the answer
– user980089
Oct 6 '11 at 16:19
If we have only one instance of class and multiple threads, is there possible to run somesynchronizedmethods concurrently?
– Sajad
Feb 15 '14 at 22:04
@ssss: Sure:staticvs non-static, usingsynchronizedblocks with different locks etc. If you need further information, please post a new question.
– NPE
Feb 15 '14 at 22:06
add a comment |
Thanks for the answer
– user980089
Oct 6 '11 at 16:19
If we have only one instance of class and multiple threads, is there possible to run somesynchronizedmethods concurrently?
– Sajad
Feb 15 '14 at 22:04
@ssss: Sure:staticvs non-static, usingsynchronizedblocks with different locks etc. If you need further information, please post a new question.
– NPE
Feb 15 '14 at 22:06
Thanks for the answer
– user980089
Oct 6 '11 at 16:19
Thanks for the answer
– user980089
Oct 6 '11 at 16:19
If we have only one instance of class and multiple threads, is there possible to run some
synchronized methods concurrently?– Sajad
Feb 15 '14 at 22:04
If we have only one instance of class and multiple threads, is there possible to run some
synchronized methods concurrently?– Sajad
Feb 15 '14 at 22:04
@ssss: Sure:
static vs non-static, using synchronized blocks with different locks etc. If you need further information, please post a new question.– NPE
Feb 15 '14 at 22:06
@ssss: Sure:
static vs non-static, using synchronized blocks with different locks etc. If you need further information, please post a new question.– NPE
Feb 15 '14 at 22:06
add a comment |
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2
The code you posted has at least one syntax error, and is really hard to read as is. Make sure you post your actual code and try to format it legibly.
– Mat
Oct 5 '11 at 10:04
The misconception is that you are locking a method, instead you have a method which locks the instance.
– Peter Lawrey
Oct 5 '11 at 10:14