From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2008-01-16 06:34:10
Frank Mori Hess wrote:
> On Tuesday 15 January 2008 20:03, Phil Endecott wrote:
>> 1. There's no "un-synchronised" version, for use in single-threaded
>> programs or when all (first) accesses come from the same thread.
>
> I took the bit in the documentation saying "implementing identical behavior
> in a single-threaded environment" to mean they are all un-synchronised, if
> you compile for example using gcc without the -pthread option.
Right, but in a large application I may have all uses of class X from a
single thread, but still with other threads in completely different
parts of the program (so I have to compile with -pthread).
>> 2. The "mutexed access" feature can be useful in situation other than
>> singletons; can't something more general-purpose be provided? I use a
>> template class Lockable<T> which grants reader/writer-exclusive access
>> to a contained T. (Reader/writer locking could be useful here.) (It
>> might be useful to make the mutex type a template parameter, with a
>> sensible default; I have a few mutexes of my own, with a
>> boost::mutex-compatible interface.)
>
> Is any of this available publically, or documentation for it available
> publically?
At http://svn.chezphil.org/libpbe/trunk/include/Locked.hh (note
Locked<T>, not Lockable<T> as I mis-wrote above):
// This provides a class template that augments a variable with a
mutex, and
// allows access only when the mutex is locked. Example:
//
// typedef Locked< vector<int> > x_t;
// x_t x;
//
// // We can only modify x via an x_t::writer:
// x_t::writer xw;
// // Creating xw locks the mutex.
// // xw behaves like a pointer to the underlying vector<int>:
// xw->push_back(123);
// xw->push_back(321);
// // The lock is released when xw goes out of scope.
//
// To read, use an x_t::reader. It behaves like a const pointer to the
// underlying data.
//
// The mutex and lock types can be specified with template parameters, but
// they default to the boost versions.
//
// I had hoped to allow conversion-to-reference for the writer and
reader, so
// that you could write xw.push_back(123) rather than xw->push_back(123).
// But this didn't work, presumably because I don't really understand how
// implict type conversion is supposed to work. My attempt is still present,
// commented out.
It looks as if it hasn't done real reader/writer locking since that
feature was removed from Boost.
As for the mutexes, I suggest that you search for my name in this
list's archive.
This is GPL licensed. Let me know if you'd prefer something else.
Regards, Phil.