Description
Concurrency primitives that may be used in a cross-process way to coordinate share memory between processes.
A small C library (libpsem) is compiled to provide portable access to semaphores (based on pyprocessing.berlios.de/). This library is then accessed using FFI to implement Ruby classes ProcessShared::Semaphore, ProcessShared::BoundedSemaphore, ProcessShared::Mutex, and ProcessShared::SharedMemory.
This is an incomplete work in progress.
License
MIT
Install
Install the gem with:
gem install process_shared
Usage
require 'process_shared'
mutex = ProcessShared::Mutex.new
mem = ProcessShared::SharedMemory.new(:int) # extends FFI::Pointer
mem.put_int(0, 0)
pid1 = fork do
puts "in process 1 (#{Process.pid})"
10.times do
sleep 0.01
mutex.synchronize do
value = mem.get_int(0)
sleep 0.01
puts "process 1 (#{Process.pid}) incrementing"
mem.put_int(0, value + 1)
end
end
end
pid2 = fork do
puts "in process 2 (#{Process.pid})"
10.times do
sleep 0.01
mutex.synchronize do
value = mem.get_int(0)
sleep 0.01
puts "process 2 (#{Process.pid}) decrementing"
mem.put_int(0, value - 1)
end
end
end
Process.wait(pid1)
Process.wait(pid2)
puts "value should be zero: #{mem.get_int(0)}"
Transfer Objects Across Processes
# allocate a sufficient memory block
mem = ProcessShared::SharedMemory.new(1024)
# sub process can write (serialize) object to memory (with bounds checking)
pid = fork do
mem.write_object(['a', 'b'])
end
Process.wait(pid)
# parent process can read the object back (synchronizing access
# with a Mutex left as an excercie to reader)
mem.read_object.must_equal ['a', 'b']
Todo
-
Test ConditionVariable
-
Implement optional override of core Thread/Mutex classes
-
Extend libpsem to win32? (See Python’s processing library)
-
Break out tests that use PSem.getvalue() (which isn’t supported on Mac OS X) so that the test suite will pass
-
Add finalizer to Mutex? (finalizer on Semaphore objects may be enough) or a method to explicitly close and release resources?
-
Test semantics of crashing processes who still hold locks, etc.
-
Is SharedArray with Enumerable mixing sufficient Array-like interface?
-
Remove bsem from libpsem as it is of little use and doesn’t work on Mac OS X
-
Possibly implement BoundedSemaphore with arbitrary bound (in Ruby rather than relying on sem_getvalue()), but this is of little utility beyond extra error checking..