Re: How to make this program more efficient?
On Sep 13, 3:18 am, Bill David <billdavi...@gmail.com> wrote:
SUBJECT: How to make this program more efficient?
In my program, a thread will check update from server
periodically and generate a stl::map for other part of this
program to read data from. Let's name the update method as
doUpdate and stl::map read methods as getData and copyData.
Since stl::map is not thread-safe, we should do
synchronization by ourselves. A usable solution is to create a
boost::mutex::scoped_lock object in all above methods to make
the access to all methods synchronized. But since the doUpdate
method will be executed periodically and the interval may be 1
hour or longer, while all other parts can only read the
stl::map, the above solution may do synchronization too much.
We only need synchronization on all methods when we are
doUpdating.
If there's any thread modifying the object, then all accesses
must be synchronized. Period. Given the usage pattern, it may
be more interesting to use a rwlock than a mutex, but this
really depends on how long the readers hold the mutex, and how
many of them there are.
Then is it possible to make this program more efficient?
Probably. Where does the profiler show that there are problems?
I have thought out some other solution like add some updating
flag. But it's not safe since stl::map may be updated when
the following part of read methods is executing. And the
operation on the flag may also be interrupted by other
threads.
You need some sort of synchronization, including for all of the
reads. (Don't forget, too, that std::map returns references to
internal data, and you need to hold the lock as long as these
references are valid.)
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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