[plt-scheme] concurrent database connections

From: Jay McCarthy (jay.mccarthy at gmail.com)
Date: Wed Mar 25 17:35:42 EDT 2009

On Wed, Mar 25, 2009 at 3:30 PM, YC <yinso.chen at gmail.com> wrote:
>> For different sessions to use the same connections, they must servlet
>> module-level definitions.
> So when web-server creates two separate threads for the same servlet module,
> does the connection get duplicated or shared?  What if the connection is
> instantiated in a module that's included by the servlet module?

All the module definitions and module imports are shared for a single
servlet module.

So, DBs created in db.ss and `db' are shared for all instances of servlet1.ss.

#lang scheme
(require "db.ss")
(define db (make-db ...))
(define (start req)
 ... uses database ...)

Suppose you also have

#lang scheme
(require "db.ss")
(define db (make-db ...))
(define (start req)
 ... uses database ...)

Anything created in "db.ss" here is NOT shared with servlet1.ss,
unless you explicitly share "db.ss" in the namespaces.

>> For different servlets to use the same connections, there must be a
>> single module that handles the connections that is shared via
>> make-servlet-namespace.
> Related to the previous question if the answer is duplicated - can
> make-servlet-namespace be used with `serve/servlet`?

Yes. See the #:servlet-namespace kw arg.


Jay McCarthy <jay at cs.byu.edu>
Assistant Professor / Brigham Young University

"The glory of God is Intelligence" - D&C 93

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