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Update README for new Mach stuff.

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Patrick Mahoney 2012-03-04 10:26:58 -06:00
parent a0b99f840f
commit 884a1fa6c3
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README.rdoc
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@ -3,11 +3,23 @@
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 http://pyprocessing.berlios.de/). This library
is then accessed using FFI to implement Ruby classes
ProcessShared::Semaphore, ProcessShared::BoundedSemaphore,
ProcessShared::Mutex, and ProcessShared::SharedMemory.
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.
@ -80,14 +92,8 @@ Install the gem with:
* 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
* 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?
* 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..