Two threads executing synchronized block simultaneously

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8
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Below is the code where a Thread enters a synchronized block, waits for 5seconds and then exits. I have started two Thread instances simultaneously.

The expectation was one of the threads will own the lock on the synchronized object & the other will wait. After 5 seconds, when the lock owner exits, the waiting thread will execute.

But, in actual, both the threads are executing the synchronized block simultaneously and also exiting at the same time.

Expected Output:

Thread-X <timeX> received the lock.
Thread-X <timeX+5s> exiting...
Thread-Y <timeY> received the lock.
Thread-Y <timeY+5s> exiting...

Actual Output:

Thread-X <time> received the lock.
Thread-Y <time> received the lock.
Thread-X <time+5s> exiting...
Thread-Y <time+5s> exiting...

Any explanation of the above behavior will be really helpful. Am I missing something here?

import java.text.SimpleDateFormat;
import java.util.Date;

public class Test2 
public static void main(String args) 
 MyRunnable m = new MyRunnable();
 Thread t = new Thread(m);
 Thread t1 = new Thread(m);
 t.start();
 t1.start();
 


class MyRunnable implements Runnable 
 @Override
 public void run() 
 synchronized (this) 
 try 
 SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss"); 
 Date date = new Date(System.currentTimeMillis());
 System.out.println(Thread.currentThread().getName() + " " + formatter.format(date) + " received the lock.");
 wait(5000);
 date = new Date(System.currentTimeMillis());
 System.out.println(Thread.currentThread().getName() + " " + formatter.format(date) + " exiting...");
 catch(InterruptedException ie)

edited 1 hour ago

Maxim Egorushkin

80.5k1195174

asked 2 hours ago

somnathchakrabarti

1,03764268

Synchronized block in the example is effectively he synchronized run() method. It's been already answered here stackoverflow.com/questions/19688666/synchronized-run-method
â€“Â dawid gdanski
2 hours ago

1

@dawidgdanski That's just plain wrong. The question uses a single object for providing the lock.
â€“Â Markus
1 hour ago

With all my knowledge on the about the synchronization I was not aware of releasing the monitor lock on wait() invocation. Thanks for correcting me.
â€“Â dawid gdanski
7 mins ago

add a commentÂ |Â

up vote
8
down vote

favorite

Below is the code where a Thread enters a synchronized block, waits for 5seconds and then exits. I have started two Thread instances simultaneously.

The expectation was one of the threads will own the lock on the synchronized object & the other will wait. After 5 seconds, when the lock owner exits, the waiting thread will execute.

But, in actual, both the threads are executing the synchronized block simultaneously and also exiting at the same time.

Expected Output:

Thread-X <timeX> received the lock.
Thread-X <timeX+5s> exiting...
Thread-Y <timeY> received the lock.
Thread-Y <timeY+5s> exiting...

Actual Output:

Thread-X <time> received the lock.
Thread-Y <time> received the lock.
Thread-X <time+5s> exiting...
Thread-Y <time+5s> exiting...

Any explanation of the above behavior will be really helpful. Am I missing something here?

import java.text.SimpleDateFormat;
import java.util.Date;

public class Test2 
public static void main(String args) 
 MyRunnable m = new MyRunnable();
 Thread t = new Thread(m);
 Thread t1 = new Thread(m);
 t.start();
 t1.start();
 


class MyRunnable implements Runnable 
 @Override
 public void run() 
 synchronized (this) 
 try 
 SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss"); 
 Date date = new Date(System.currentTimeMillis());
 System.out.println(Thread.currentThread().getName() + " " + formatter.format(date) + " received the lock.");
 wait(5000);
 date = new Date(System.currentTimeMillis());
 System.out.println(Thread.currentThread().getName() + " " + formatter.format(date) + " exiting...");
 catch(InterruptedException ie)

edited 1 hour ago

Maxim Egorushkin

80.5k1195174

asked 2 hours ago

somnathchakrabarti

1,03764268

Synchronized block in the example is effectively he synchronized run() method. It's been already answered here stackoverflow.com/questions/19688666/synchronized-run-method
â€“Â dawid gdanski
2 hours ago

1

@dawidgdanski That's just plain wrong. The question uses a single object for providing the lock.
â€“Â Markus
1 hour ago

With all my knowledge on the about the synchronization I was not aware of releasing the monitor lock on wait() invocation. Thanks for correcting me.
â€“Â dawid gdanski
7 mins ago

add a commentÂ |Â

up vote
8
down vote

favorite

Below is the code where a Thread enters a synchronized block, waits for 5seconds and then exits. I have started two Thread instances simultaneously.

The expectation was one of the threads will own the lock on the synchronized object & the other will wait. After 5 seconds, when the lock owner exits, the waiting thread will execute.

But, in actual, both the threads are executing the synchronized block simultaneously and also exiting at the same time.

Expected Output:

Thread-X <timeX> received the lock.
Thread-X <timeX+5s> exiting...
Thread-Y <timeY> received the lock.
Thread-Y <timeY+5s> exiting...

Actual Output:

Thread-X <time> received the lock.
Thread-Y <time> received the lock.
Thread-X <time+5s> exiting...
Thread-Y <time+5s> exiting...

Any explanation of the above behavior will be really helpful. Am I missing something here?

import java.text.SimpleDateFormat;
import java.util.Date;

public class Test2 
public static void main(String args) 
 MyRunnable m = new MyRunnable();
 Thread t = new Thread(m);
 Thread t1 = new Thread(m);
 t.start();
 t1.start();
 


class MyRunnable implements Runnable 
 @Override
 public void run() 
 synchronized (this) 
 try 
 SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss"); 
 Date date = new Date(System.currentTimeMillis());
 System.out.println(Thread.currentThread().getName() + " " + formatter.format(date) + " received the lock.");
 wait(5000);
 date = new Date(System.currentTimeMillis());
 System.out.println(Thread.currentThread().getName() + " " + formatter.format(date) + " exiting...");
 catch(InterruptedException ie)

edited 1 hour ago

Maxim Egorushkin

80.5k1195174

asked 2 hours ago

somnathchakrabarti

1,03764268

Below is the code where a Thread enters a synchronized block, waits for 5seconds and then exits. I have started two Thread instances simultaneously.

The expectation was one of the threads will own the lock on the synchronized object & the other will wait. After 5 seconds, when the lock owner exits, the waiting thread will execute.

But, in actual, both the threads are executing the synchronized block simultaneously and also exiting at the same time.

Expected Output:

Thread-X <timeX> received the lock.
Thread-X <timeX+5s> exiting...
Thread-Y <timeY> received the lock.
Thread-Y <timeY+5s> exiting...

Actual Output:

Thread-X <time> received the lock.
Thread-Y <time> received the lock.
Thread-X <time+5s> exiting...
Thread-Y <time+5s> exiting...

Any explanation of the above behavior will be really helpful. Am I missing something here?

import java.text.SimpleDateFormat;
import java.util.Date;

public class Test2 
public static void main(String args) 
 MyRunnable m = new MyRunnable();
 Thread t = new Thread(m);
 Thread t1 = new Thread(m);
 t.start();
 t1.start();
 


class MyRunnable implements Runnable 
 @Override
 public void run() 
 synchronized (this) 
 try 
 SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss"); 
 Date date = new Date(System.currentTimeMillis());
 System.out.println(Thread.currentThread().getName() + " " + formatter.format(date) + " received the lock.");
 wait(5000);
 date = new Date(System.currentTimeMillis());
 System.out.println(Thread.currentThread().getName() + " " + formatter.format(date) + " exiting...");
 catch(InterruptedException ie)

java multithreading synchronized thread-synchronization

edited 1 hour ago

Maxim Egorushkin

80.5k1195174

asked 2 hours ago

somnathchakrabarti

1,03764268

edited 1 hour ago

Maxim Egorushkin

80.5k1195174

asked 2 hours ago

somnathchakrabarti

1,03764268

edited 1 hour ago

Maxim Egorushkin

80.5k1195174

edited 1 hour ago

Maxim Egorushkin

80.5k1195174

edited 1 hour ago

Maxim Egorushkin

80.5k1195174

asked 2 hours ago

somnathchakrabarti

1,03764268

asked 2 hours ago

somnathchakrabarti

1,03764268

asked 2 hours ago

somnathchakrabarti

1,03764268

Synchronized block in the example is effectively he synchronized run() method. It's been already answered here stackoverflow.com/questions/19688666/synchronized-run-method
â€“Â dawid gdanski
2 hours ago

1

@dawidgdanski That's just plain wrong. The question uses a single object for providing the lock.
â€“Â Markus
1 hour ago

With all my knowledge on the about the synchronization I was not aware of releasing the monitor lock on wait() invocation. Thanks for correcting me.
â€“Â dawid gdanski
7 mins ago

add a commentÂ |Â

Synchronized block in the example is effectively he synchronized run() method. It's been already answered here stackoverflow.com/questions/19688666/synchronized-run-method
â€“Â dawid gdanski
2 hours ago

1

@dawidgdanski That's just plain wrong. The question uses a single object for providing the lock.
â€“Â Markus
1 hour ago

With all my knowledge on the about the synchronization I was not aware of releasing the monitor lock on wait() invocation. Thanks for correcting me.
â€“Â dawid gdanski
7 mins ago

Synchronized block in the example is effectively he synchronized run() method. It's been already answered here stackoverflow.com/questions/19688666/synchronized-run-method
â€“Â dawid gdanski
2 hours ago

@dawidgdanski That's just plain wrong. The question uses a single object for providing the lock.
â€“Â Markus
1 hour ago

With all my knowledge on the about the synchronization I was not aware of releasing the monitor lock on wait() invocation. Thanks for correcting me.
â€“Â dawid gdanski
7 mins ago

add a commentÂ |Â

3 Answers
3

active

oldest

votes

up vote
11
down vote

The answer lies here: https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#wait(long)

Quote:

[...] This method causes the current thread (call it T) to place itself in the wait set for this object and then to relinquish any and all synchronization claims on this object. [...]

edited 53 mins ago

Hulk

2,14411432

answered 1 hour ago

Markus

2,07121121

add a commentÂ |Â

up vote
2
down vote

Use

Thread.sleep(5000);

JavaDocs for Thread.sleep:

Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers. The thread does not lose ownership of any monitors.

edited 49 mins ago

Hulk

2,14411432

answered 1 hour ago

Selindek

38419

add a commentÂ |Â

up vote
1
down vote

Guarded Blocks:

When wait is invoked, the thread releases the lock and suspends
execution.

Only one thread can execute a synchronized block guarded by the same object! Calling wait(...) in your example releases the lock, thus allowing another thread to acquire the lock.

edited 47 mins ago

answered 1 hour ago

Oleksandr

6,91833365

add a commentÂ |Â

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3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

up vote
11
down vote

The answer lies here: https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#wait(long)

Quote:

[...] This method causes the current thread (call it T) to place itself in the wait set for this object and then to relinquish any and all synchronization claims on this object. [...]

edited 53 mins ago

Hulk

2,14411432

answered 1 hour ago

Markus

2,07121121

add a commentÂ |Â

up vote
11
down vote

The answer lies here: https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#wait(long)

Quote:

[...] This method causes the current thread (call it T) to place itself in the wait set for this object and then to relinquish any and all synchronization claims on this object. [...]

edited 53 mins ago

Hulk

2,14411432

answered 1 hour ago

Markus

2,07121121

add a commentÂ |Â

up vote
11
down vote

The answer lies here: https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#wait(long)

Quote:

[...] This method causes the current thread (call it T) to place itself in the wait set for this object and then to relinquish any and all synchronization claims on this object. [...]

edited 53 mins ago

Hulk

2,14411432

answered 1 hour ago

Markus

2,07121121

The answer lies here: https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#wait(long)

Quote:

[...] This method causes the current thread (call it T) to place itself in the wait set for this object and then to relinquish any and all synchronization claims on this object. [...]

edited 53 mins ago

Hulk

2,14411432

answered 1 hour ago

Markus

2,07121121

edited 53 mins ago

Hulk

2,14411432

edited 53 mins ago

Hulk

2,14411432

edited 53 mins ago

Hulk

2,14411432

answered 1 hour ago

Markus

2,07121121

answered 1 hour ago

Markus

2,07121121

answered 1 hour ago

Markus

2,07121121

add a commentÂ |Â

up vote
2
down vote

Use

Thread.sleep(5000);

JavaDocs for Thread.sleep:

Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers. The thread does not lose ownership of any monitors.

edited 49 mins ago

Hulk

2,14411432

answered 1 hour ago

Selindek

38419

add a commentÂ |Â

up vote
2
down vote

Use

Thread.sleep(5000);

JavaDocs for Thread.sleep:

Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers. The thread does not lose ownership of any monitors.

edited 49 mins ago

Hulk

2,14411432

answered 1 hour ago

Selindek

38419

add a commentÂ |Â

up vote
2
down vote

Use

Thread.sleep(5000);

JavaDocs for Thread.sleep:

Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers. The thread does not lose ownership of any monitors.

edited 49 mins ago

Hulk

2,14411432

answered 1 hour ago

Selindek

38419

Use

Thread.sleep(5000);

JavaDocs for Thread.sleep:

Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers. The thread does not lose ownership of any monitors.

edited 49 mins ago

Hulk

2,14411432

answered 1 hour ago

Selindek

38419

edited 49 mins ago

Hulk

2,14411432

edited 49 mins ago

Hulk

2,14411432

edited 49 mins ago

Hulk

2,14411432

answered 1 hour ago

Selindek

38419

answered 1 hour ago

Selindek

38419

answered 1 hour ago

Selindek

38419

add a commentÂ |Â

up vote
1
down vote

Guarded Blocks:

When wait is invoked, the thread releases the lock and suspends
execution.

Only one thread can execute a synchronized block guarded by the same object! Calling wait(...) in your example releases the lock, thus allowing another thread to acquire the lock.

edited 47 mins ago

answered 1 hour ago

Oleksandr

6,91833365

add a commentÂ |Â

up vote
1
down vote

Guarded Blocks:

When wait is invoked, the thread releases the lock and suspends
execution.

Only one thread can execute a synchronized block guarded by the same object! Calling wait(...) in your example releases the lock, thus allowing another thread to acquire the lock.

edited 47 mins ago

answered 1 hour ago

Oleksandr

6,91833365

add a commentÂ |Â

up vote
1
down vote

Guarded Blocks:

When wait is invoked, the thread releases the lock and suspends
execution.

Only one thread can execute a synchronized block guarded by the same object! Calling wait(...) in your example releases the lock, thus allowing another thread to acquire the lock.

edited 47 mins ago

answered 1 hour ago

Oleksandr

6,91833365

Guarded Blocks:

When wait is invoked, the thread releases the lock and suspends
execution.

Only one thread can execute a synchronized block guarded by the same object! Calling wait(...) in your example releases the lock, thus allowing another thread to acquire the lock.

edited 47 mins ago

answered 1 hour ago

Oleksandr

6,91833365

edited 47 mins ago

answered 1 hour ago

Oleksandr

6,91833365

answered 1 hour ago

Oleksandr

6,91833365

answered 1 hour ago

Oleksandr

6,91833365

add a commentÂ |Â

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