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