Want to protect your cyber security and still get fast solutions? Ask a secure question today.Go Premium

x
?
Solved

concurrent access to static methods

Posted on 2000-04-11
4
Medium Priority
?
3,023 Views
Last Modified: 2009-07-25
Hey,
What happens during concurrent access (from different threads) to a static method?

Do I need to synchronize the method in order to prevent a mess?

yuval.
0
Comment
Question by:yuvalg
  • 2
4 Comments
 
LVL 16

Accepted Solution

by:
imladris earned 100 total points
ID: 2704554
In general, any method that changes state information (i.e. non local variables) needs to be synchronized in order to be thread safe. The only difference between a "regular" method and a static method, is that a static method tends to access static (global) variables, and it must be synchronized in a global, not an instance, fashion.

So, yes, if your static method changes the value of global variables, or even member variables of existing classes, you will need to synchronize it. If it purely and only manipulates local values (such as Integer.parseInt would do for instance), then it is not necessary.
0
 
LVL 19

Expert Comment

by:Jim Cakalic
ID: 2704592
There is no automatic multi-threaded protection inherent to a static method. A static method is just like an instance method except that it operates on a set of fields for which there can only be one instance in the JVM.

As for whether synchronization is needed or not, this comes down to whether the method is changing the state of static data on which it operates and whether it does so atomically. Atomic operations are those that the VM can guarantee will be non-interruptible.

As you might guess, there ain't a lot of guaranteed atomic operations. Unless you are operating exclusively with primitive datatypes (excluding double and long) and performing simple single VM instructions like pre-increment (++), what you are doing is not atomic. Even incrementing a long value is not atomic as it requires more than one VM instruction to implement. That means it would be possible (even if not highly probable) that a thread in the middle of changing the value of the long could be interrupted by another thread which, retrieving the value of the same long, now gets a corrupt value.

So ... good for you for thinking about multi-threaded issues. If you believe the best design is to have static methods but the underlying class fields on which these operate are not immutable, then by all means synchronize the methods or synchronize on one or more of the object fields as needed. Synchronizing methods will force single-threading through all the synchronized methods of the class. Synchronizing on object fields will allow concurrent thread access to discrete subsets of the class data. However, beware this because you can introduce thread deadlock.

Hope I haven't scared you off completely. Threading is a powerful Java capability. Powerful both in solving problems and introducing new ones.

Best regards,
Jim Cakalic

0
 
LVL 3

Author Comment

by:yuvalg
ID: 2705302
I get it.
Your main idea of static method is not accurate though.
 As i understand it, static methods are not solely dedicated to accessing static methods.
They are used to perform "any non class-variable manipulation" as done in the java Integer class.

What still remains a mistery (to me :) is how to declare static methods within an interface.
Buts thats another question and ill offer points after i do some digging of my own.

Thanks all.

0
 
LVL 16

Expert Comment

by:imladris
ID: 2705386
You're quite right, static methods are note SOLELY for the purpose of accessing static methods. But since your question was about static (presumably as opposed to instance) methods, my answer referenced a static methods TENDENCY to access other static methods and variables. You'll note that the last line:

"So, yes, if your static method changes the value of global variables, or even member variables of existing classes..."

does in fact acknowledge the possibility. I didn't explore it in detail since it is a side issue to synchronization and threadsafety, in the sense that whether a static method accesses member variables or not doesn't change the answer about the need for synchronization. My apologies for any confusion I caused.

0

Featured Post

[Webinar On Demand] Database Backup and Recovery

Does your company store data on premises, off site, in the cloud, or a combination of these? If you answered “yes”, you need a data backup recovery plan that fits each and every platform. Watch now as as Percona teaches us how to build agile data backup recovery plan.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

An old method to applying the Singleton pattern in your Java code is to check if a static instance, defined in the same class that needs to be instantiated once and only once, is null and then create a new instance; otherwise, the pre-existing insta…
For beginner Java programmers or at least those new to the Eclipse IDE, the following tutorial will show some (four) ways in which you can import your Java projects to your Eclipse workbench. Introduction While learning Java can be done with…
Viewers learn how to read error messages and identify possible mistakes that could cause hours of frustration. Coding is as much about debugging your code as it is about writing it. Define Error Message: Line Numbers: Type of Error: Break Down…
Viewers will learn about if statements in Java and their use The if statement: The condition required to create an if statement: Variations of if statements: An example using if statements:
Suggested Courses
Course of the Month14 days, 12 hours left to enroll

578 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question