How to do inter-process locking with forked Ruby processes? -

objective

increment counter using ruby's fork method , several workers

disclaimers

• i not want use external dependencies this
• usage of ruby's thread class not allowed
• i want see if possible using fork

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here's little shared memory mock

class memory   def self.address= value     @value = value   end    def self.address     @value   end end 

here's worker

class worker   def initialize mutex     @mutex = mutex   end    def work     @mutex.synchronize       print "begin: %d " % (tmp=memory.address)       sleep 0.05       print "end: %d \n" % (memory.address = tmp + 1)     end   end end 

let's run it

# init memory.address = 0 mutex = mutex.new  # create workers workers = [] 10.times   workers << fork     worker.new(mutex).work   end end  # wait workers finish process.waitall 

output

begin: 0 begin: 0 begin: 0 begin: 0 begin: 0 begin: 0 begin: 0 begin: 0 begin: 0 begin: 0 end: 1 end: 1 end: 1 end: 1 end: 1 end: 1 end: 1 end: 1 end: 1 end: 1 

expected output

begin: 0 end: 1 begin: 1 end: 2 begin: 2 end: 3 begin: 3 end: 4 begin: 4 end: 5 begin: 5 end: 6 begin: 6 end: 7 begin: 7 end: 8 begin: 8 end: 9 begin: 9 end: 10 

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side questions:

• am supposed using single mutex?
• does matter if each worker creates own mutex?

forked processes inherit parent's resources memory copy (or copy on write): changes made in 1 process have no effect on other ones.

similarly each process has own copy of mutex, calls synchronise don't achieve anything.

if need communicate child processes, 1 way use pipe (see docs io). each process inherits copy of pipe , writes 1 process show in other process.

child_in, parent_out = io.pipe parent_in, child_out = io.pipe  process.fork   parent_out.close   parent_in.close   #data written child_out appears on parent_in in parent process   #reading child_in returns data parent has written parent_out end child_read.close child_write.close  #write data parent_out here have appear on child_in in child #reading parent_in data child has written child_out 

as far know there no cross process concurrency primitives built ruby.