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).