PureBasic Forums - English

Is it possible to pass a linked list as a parameter to a thread?

Shouldnt something simple like this work?

didn't work.
I wan't the thread to have access to the linked list. Should i just use a global linked list?

AFAIK the supported parameter you can pass to a thread it's a number.

It can be used the way you like, even as a pointer. But lists, maps, etc, all have a dedicate keyword to be used in the receiving procedure, and only using that keyword you can then use the PB commands to access/modify the list, map, etc.

So I would say you can't pass them to a thread and you have to declare them as global to access them, using a mutex if needed.

Different would be with a list you made using pointers and some code you wrote to manage it. You would need only a pointer then.

I am going to go with a global list and mutex, thank you

use a list inside a structure:

STARGÅTE wrote:use a list inside a structure:

Code: Select all

Structure Packets
  string.s
EndStructure

Structure PacketsList
	List Packet.Packets()
EndStructure

Define PacketsList.PacketsList

AddElement(PacketsList\Packet())
PacketsList\Packet()\string = "hi"


Thanks Stargate  :D Do i still need to use a mutex if i am manipulating the list outside of the thread?
Procedure Network(*PacketsList.PacketsList)
  Debug *PacketsList\Packet()\string
  AddElement(*PacketsList\Packet())
  *PacketsList\Packet()\string = "next hi"
EndProcedure

Define Thread = CreateThread(@Network(), @PacketsList)

WaitThread(Thread)

Debug "--"
ForEach PacketsList\Packet()
	Debug PacketsList\Packet()\string
Next

Thanks Stargate. If i am manipulating the list outside of the thread, do i need to use mutex?

Thanks Stargate. If i am manipulating the list outside of the thread, do i need to use mutex?

The mutex is needed if you access the list from more than one thread and not in readonly mode.
It's needed if at least one thread is modifying the list and some other thread is reading or modifying it too.

Just imagine to NOT use a mutex. Can some of your code running in a thread find itself reading some wrong data because another thread is halfway to complete an alteration to the same data ? If the answer is yes, than you need a mutex.

luis wrote:

Thanks Stargate. If i am manipulating the list outside of the thread, do i need to use mutex?

The mutex is needed if you access the list from more than one thread and not in readonly mode.
It's needed if at least one thread is modifying the list and some other thread is reading or modifying it too.

Just imagine to NOT use a mutex. Can some of your code running in a thread find itself reading some wrong data because another thread is halfway to complete an alteration to the same data ? If the answer is yes, than you need a mutex.

Thanks for the confirmation.

luis wrote:

Thanks Stargate. If i am manipulating the list outside of the thread, do i need to use mutex?

The mutex is needed if you access the list from more than one thread and not in readonly mode.

If a linked list is accessed by two threads, regardless if
only read and/or write, it needs mutexprotection. A linked
list has only one possible current element, so if one
thread reads one element and the other wants to read
another element ... it will result in undefined results.

MFG PMV

@PMV

Yes, I have overlooked that, thank you

The fact is the list contains "states" even if data is not modified.

From the point of view of a thread even if the user-data is not changed in read-only mode, internal states can change, so there is some "change" to the data-structure. That's enough to create havoc.

@AndyMK: I apologize for the imprecision.

luis wrote:@PMV

Yes, I have overlooked that, thank you

The fact is the list contains "states" even if data is not modified.

From the point of view of a thread even if the user-data is not changed in read-only mode, internal states can change, so there is some "change" to the data-structure. That's enough to create havoc.

@AndyMK: I apologize for the imprecision.

no probs, i got it working