i would like to know how to work with Threads in squeak smalltlak
b1 := Ball new.
b2 := Ball new.
this 2 next objects should run in different Threads together(Multi threading). how can i do it ?
"Thread 1"
b1 start:210 at:210. "start is the name of the method"
"Thread 2"
b2 start:310 at:210.
First of all, the Squeak VM only offers green threads, i.e. the VM runs in a single process and threads are simulated inside this single process.
To use threads (simply called processes in Squeak) you usually send the message #fork or #forkAt: to a block:
[ b1 start: 210 at: 210 ] fork.
[ b1 start: 210 at: 210 ] forkAt: Processor userBackgroundPriority.
That's all there is to it really, unless you need facilities for inter process communication. Then you can use a Mutex for critical sections (only one process can be in this section at a time) or a Semaphore for controlling access to a shared resource:
"before critical section"
self mutex critical: [ "critical section" ].
"after critical section"
"access shared resource"
self semaphore wait.
"do stuff..."
"release shared resource"
self semaphore signal.
The methods #semaphore and #mutex are simply accessors to variables. These variables should not be initialised lazily but before multiple processes may call the methods. That usually means you'll initialise them in the #initialize method:
initialize
semaphore := Semaphore new.
mutex := Mutex new.
The reason for this is that you can not guarantee that a process will not be suspended in the #ifNil: block. This could result in two processes using two different mutexes / semaphores.
If you need more information, you should take a look at the Deep into Pharo book and maybe read the original Smalltalk books by Adele Goldberg (available at your favourite online book store).
And you should of course be careful about the interactions between your threads and the UI.
You might not need threads, you can also use stepping in Morphic.
