Quoting David Erickson <[EMAIL PROTECTED]>: > Hey I have been reading a lot about threading lately from the JLS and > otherwise.. but my question is what would be an example of a non-threadsafe > action? Struts manual said that only one instance of an action exists in > the JVM.. and when I run an action each thread creates its own versions of > all the variables within the action correct?
More precisely, you get per-thread *local* variables (i.e. those defined inside a method). If you use *instance* variables (those defined in the class, rather than inside the method, there is only one copy of those variables -- and you get in trouble if you use those variables to store information that is specific to a particular request. > So assuming I'm not accessing > some outside 'global' variable, everything is inherintly threadsafe right? > > If anyone can give me an example of what 'not' to do that would help > tremendously. > thanks, > David > Consider the LogonAction class in the struts-example app. Note that the "username" and "password" variables are defined inside the execute() method, so they are local variables (and therefore have a copy per thread). What would happen to your logon processing if you moved those variable declarations to be outside the method instead of inside? Then, if you had two people logging on at the same time, the single copy of the username and password variables would be at risk for getting scribbled on by the second user. The most important rule for thread safety is to use local variables to store anything that is specific to a particular request (using instance variables to store read-only copies of things needed by multiple requests, on the other hand, is fine). Craig --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
