Beefy Boxes and Bandwidth Generously Provided by pair Networks
Problems? Is your data what you think it is?
 
PerlMonks  

Re: threads::shared variables not really shared... or are they?

by renodino (Curate)
on Mar 06, 2008 at 23:51 UTC ( [id://672632]=note: print w/replies, xml ) Need Help??


in reply to threads::shared variables not really shared... or are they?

Shared scalars, arrays, and hashes are indeed shared, but via tied proxy mechanism. The actual data resides in a shared Perl interpretter context; the usual tie() operations then route all reads/writes (and various metadata operations) to execute against the shared interpretter's version of the variables. Note that, for scalars, the shared value does get copied into the private proxy on read().

I can't say precisely why your example doesn't grow significantly, except that the array tie() operations won't populate the private proxy copy in each thread, instead routing directly to the shared interpretter's version of the array. So in your example, the private @a never grows, only the shared version.

Note that if you were vivifying individual shared scalars, you likely would see some significant memory growth, since there would be a copy in both the originating thread, and in the shared interpretter.

Also note that the shared interpretter is one of the major bottlenecks in ithreads: as you might imagine, a Perl interpretter context holds a lot of state, thus concurrent access requires a major lock on the whole thing...which unfortunately can create a lot of thread contention.


Perl Contrarian & SQL fanboy

Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?
Node Status?
node history
Node Type: note [id://672632]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this?Last hourOther CB clients
Other Users?
Others perusing the Monastery: (6)
As of 2024-03-28 19:12 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    No recent polls found