100 lines
2.9 KiB
Plaintext
100 lines
2.9 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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FFI is used to access POSIX semaphore on Linux or Mach semaphores on
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Mac. Atop these semaphores are implemented ProcessShared::Semaphore,
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ProcessShared::Mutex. POSIX shared memory is used to implement
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ProcessShared::SharedMemory.
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On Linux, POSIX semaphores support <tt>sem_timedwait()</tt> which can wait on
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a semaphore but stop waiting after a timeout.
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Mac OS X's implementation of POSIX semaphores does not support
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timeouts. But, the Mach layer in Mac OS X has its own semaphores that
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do support timeouts. Thus, process_shared implements a moderate
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subset of the Mach API, which is quite a bit different from POSIX.
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Namely, semaphores created in one process are not available in child
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processes created via <tt>fork()</tt>. Mach does provide the means to copy
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capabilities between tasks (Mach equivalent to processes).
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process_shared overrides Ruby's <tt>fork</tt> methods so that semaphores are
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copied from parent to child to emulate the POSIX behavior.
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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 to win32? (See Python's processing library)
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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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