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