Updating a local variable within new threads
I am working on designing a multi-user application and would like to have a singleton service class that is shared amongst all of the user threads.
Within this class, I would like to have a method that does some heavy lifting to eventually compile a seperate list for each user, I am under the impression that since this is a method, each user thread will recieve its own sperate copy of this on its call stack.
Since this process is time consuming, I would like create multiple threads within the method to handle the processing and add items to a single list that was declared and instantiated within the method.
In the end I am envisioning a list complete list for each user that will then be able to be used throughout the rest of the application within the users thread.
My question is: How do accomplish sharing the list declared in the method amongst the multiple threads I want to create within the method while maintaining thread safety?
The flow chart below may explain everything better
java multithreading
asked Nov 15 '18 at 2:01
oznomaloznomal
71111
|
show 2 more comments
I am working on designing a multi-user application and would like to have a singleton service class that is shared amongst all of the user threads.
Within this class, I would like to have a method that does some heavy lifting to eventually compile a seperate list for each user, I am under the impression that since this is a method, each user thread will recieve its own sperate copy of this on its call stack.
Since this process is time consuming, I would like create multiple threads within the method to handle the processing and add items to a single list that was declared and instantiated within the method.
In the end I am envisioning a list complete list for each user that will then be able to be used throughout the rest of the application within the users thread.
My question is: How do accomplish sharing the list declared in the method amongst the multiple threads I want to create within the method while maintaining thread safety?
The flow chart below may explain everything better
java multithreading
asked Nov 15 '18 at 2:01
oznomaloznomal
71111
Why not use aFuture, implement the task, and avoid the issues of the Singleton?
– KevinO
Nov 15 '18 at 2:02
Local variables are only visible to one thread at a time, so they're normally used to isolate data that isn't shared between threads. To publish a local variable where other threads can see it, use Safe Publication: stackoverflow.com/questions/801993/…
– markspace
Nov 15 '18 at 2:34
Don't get confused though. If a local variable is a method parameter and that value was copied from some part of the code that is already public and visible to other threads, then (obviously) that data is shared. Only data/objects created locally is not shared.
– markspace
Nov 15 '18 at 2:37
Since the list represents something, I'd suggest making a class for that purpose. The list would then be defined as a thread safe instance variable. stackoverflow.com/questions/8203864/…
– robertf
Nov 15 '18 at 2:50
Well, we know next to nothing about the OP's actual problem, so I think it's a little premature to suggest implementations. I was going to suggest that the list be made not an instance variable, that it be kept local, and simple pass a reference to the specific threads that need to know about it. But I really don't know, because the OP's problem is so vague and general. The whole thing could be IO bound for example, and then threads don't help.
– markspace
Nov 15 '18 at 2:56
|
show 2 more comments
I am working on designing a multi-user application and would like to have a singleton service class that is shared amongst all of the user threads.
Within this class, I would like to have a method that does some heavy lifting to eventually compile a seperate list for each user, I am under the impression that since this is a method, each user thread will recieve its own sperate copy of this on its call stack.
Since this process is time consuming, I would like create multiple threads within the method to handle the processing and add items to a single list that was declared and instantiated within the method.
In the end I am envisioning a list complete list for each user that will then be able to be used throughout the rest of the application within the users thread.
My question is: How do accomplish sharing the list declared in the method amongst the multiple threads I want to create within the method while maintaining thread safety?
The flow chart below may explain everything better
java multithreading
asked Nov 15 '18 at 2:01
oznomaloznomal
71111
I am working on designing a multi-user application and would like to have a singleton service class that is shared amongst all of the user threads.
Within this class, I would like to have a method that does some heavy lifting to eventually compile a seperate list for each user, I am under the impression that since this is a method, each user thread will recieve its own sperate copy of this on its call stack.
Since this process is time consuming, I would like create multiple threads within the method to handle the processing and add items to a single list that was declared and instantiated within the method.
In the end I am envisioning a list complete list for each user that will then be able to be used throughout the rest of the application within the users thread.
My question is: How do accomplish sharing the list declared in the method amongst the multiple threads I want to create within the method while maintaining thread safety?
The flow chart below may explain everything better
java multithreading
java multithreading
asked Nov 15 '18 at 2:01
oznomaloznomal
71111
asked Nov 15 '18 at 2:01
oznomaloznomal
71111
asked Nov 15 '18 at 2:01
oznomaloznomal
71111
asked Nov 15 '18 at 2:01
oznomaloznomal
71111
asked Nov 15 '18 at 2:01
oznomaloznomal
71111
71111
Why not use aFuture, implement the task, and avoid the issues of the Singleton?
– KevinO
Nov 15 '18 at 2:02
Local variables are only visible to one thread at a time, so they're normally used to isolate data that isn't shared between threads. To publish a local variable where other threads can see it, use Safe Publication: stackoverflow.com/questions/801993/…
– markspace
Nov 15 '18 at 2:34
Don't get confused though. If a local variable is a method parameter and that value was copied from some part of the code that is already public and visible to other threads, then (obviously) that data is shared. Only data/objects created locally is not shared.
– markspace
Nov 15 '18 at 2:37
Since the list represents something, I'd suggest making a class for that purpose. The list would then be defined as a thread safe instance variable. stackoverflow.com/questions/8203864/…
– robertf
Nov 15 '18 at 2:50
Well, we know next to nothing about the OP's actual problem, so I think it's a little premature to suggest implementations. I was going to suggest that the list be made not an instance variable, that it be kept local, and simple pass a reference to the specific threads that need to know about it. But I really don't know, because the OP's problem is so vague and general. The whole thing could be IO bound for example, and then threads don't help.
– markspace
Nov 15 '18 at 2:56
|
show 2 more comments
Why not use aFuture, implement the task, and avoid the issues of the Singleton?
– KevinO
Nov 15 '18 at 2:02
Local variables are only visible to one thread at a time, so they're normally used to isolate data that isn't shared between threads. To publish a local variable where other threads can see it, use Safe Publication: stackoverflow.com/questions/801993/…
– markspace
Nov 15 '18 at 2:34
Don't get confused though. If a local variable is a method parameter and that value was copied from some part of the code that is already public and visible to other threads, then (obviously) that data is shared. Only data/objects created locally is not shared.
– markspace
Nov 15 '18 at 2:37
Since the list represents something, I'd suggest making a class for that purpose. The list would then be defined as a thread safe instance variable. stackoverflow.com/questions/8203864/…
– robertf
Nov 15 '18 at 2:50
Well, we know next to nothing about the OP's actual problem, so I think it's a little premature to suggest implementations. I was going to suggest that the list be made not an instance variable, that it be kept local, and simple pass a reference to the specific threads that need to know about it. But I really don't know, because the OP's problem is so vague and general. The whole thing could be IO bound for example, and then threads don't help.
– markspace
Nov 15 '18 at 2:56
Why not use a
Future, implement the task, and avoid the issues of the Singleton?– KevinO
Nov 15 '18 at 2:02
Why not use a
Future, implement the task, and avoid the issues of the Singleton?– KevinO
Nov 15 '18 at 2:02
Local variables are only visible to one thread at a time, so they're normally used to isolate data that isn't shared between threads. To publish a local variable where other threads can see it, use Safe Publication: stackoverflow.com/questions/801993/…
– markspace
Nov 15 '18 at 2:34
Local variables are only visible to one thread at a time, so they're normally used to isolate data that isn't shared between threads. To publish a local variable where other threads can see it, use Safe Publication: stackoverflow.com/questions/801993/…
– markspace
Nov 15 '18 at 2:34
Don't get confused though. If a local variable is a method parameter and that value was copied from some part of the code that is already public and visible to other threads, then (obviously) that data is shared. Only data/objects created locally is not shared.
– markspace
Nov 15 '18 at 2:37
Don't get confused though. If a local variable is a method parameter and that value was copied from some part of the code that is already public and visible to other threads, then (obviously) that data is shared. Only data/objects created locally is not shared.
– markspace
Nov 15 '18 at 2:37
Since the list represents something, I'd suggest making a class for that purpose. The list would then be defined as a thread safe instance variable. stackoverflow.com/questions/8203864/…
– robertf
Nov 15 '18 at 2:50
Since the list represents something, I'd suggest making a class for that purpose. The list would then be defined as a thread safe instance variable. stackoverflow.com/questions/8203864/…
– robertf
Nov 15 '18 at 2:50
Well, we know next to nothing about the OP's actual problem, so I think it's a little premature to suggest implementations. I was going to suggest that the list be made not an instance variable, that it be kept local, and simple pass a reference to the specific threads that need to know about it. But I really don't know, because the OP's problem is so vague and general. The whole thing could be IO bound for example, and then threads don't help.
– markspace
Nov 15 '18 at 2:56
Well, we know next to nothing about the OP's actual problem, so I think it's a little premature to suggest implementations. I was going to suggest that the list be made not an instance variable, that it be kept local, and simple pass a reference to the specific threads that need to know about it. But I really don't know, because the OP's problem is so vague and general. The whole thing could be IO bound for example, and then threads don't help.
– markspace
Nov 15 '18 at 2:56
|
show 2 more comments
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Why not use a
Future, implement the task, and avoid the issues of the Singleton?– KevinO
Nov 15 '18 at 2:02
Local variables are only visible to one thread at a time, so they're normally used to isolate data that isn't shared between threads. To publish a local variable where other threads can see it, use Safe Publication: stackoverflow.com/questions/801993/…
– markspace
Nov 15 '18 at 2:34
Don't get confused though. If a local variable is a method parameter and that value was copied from some part of the code that is already public and visible to other threads, then (obviously) that data is shared. Only data/objects created locally is not shared.
– markspace
Nov 15 '18 at 2:37
Since the list represents something, I'd suggest making a class for that purpose. The list would then be defined as a thread safe instance variable. stackoverflow.com/questions/8203864/…
– robertf
Nov 15 '18 at 2:50
Well, we know next to nothing about the OP's actual problem, so I think it's a little premature to suggest implementations. I was going to suggest that the list be made not an instance variable, that it be kept local, and simple pass a reference to the specific threads that need to know about it. But I really don't know, because the OP's problem is so vague and general. The whole thing could be IO bound for example, and then threads don't help.
– markspace
Nov 15 '18 at 2:56