FW: environment independent time functions...

Sept. 30, 2010

      I'm forwarding this message from Christos Zoulas, who is not on the time zone mailing list. Those of you who are on the list, please direct replies appropriately.

				--ado

-----Original Message-----
From: Christos Zoulas [mailto:christos@zoulas.com] 
Sent: Thursday, September 30, 2010 4:36
To: tz@lecserver.nci.nih.gov
Subject: environment independent time functions...

Hello,

What I want to achieve is to be able to use the time functions in a
multi-threaded program that can handle multiple timezones at the same
time. Right now, this is impossible, because the notion of timezone is
expressed through the environment. I was careful to re-use the existing
code and not change existing functionality so the following routines
are just an add-on.

I modified tzcode 2010l to add the following functions (as defined in
timeextra.h).

First I expose an opaque timezone type:

    typedef struct __state *timezone_t;

which is no other than the internal state.

Then I provide a way to allocate the handle on per timezone name and to
free it.

    const timezone_t	tzalloc(const char *);
    void		tzfree(const timezone_t);

Note that the handle is const, because I might want to enhance this in
the future to use reference counting instead of allocating a new one
per invocation.

Then I provide a way to return the two (dst and nondst) strings (like
tzname[0], and tzname[1]) with:

    const char *	tzgetname(const timezone_t, int);

The following functions are also provided, which are like the _r counterparts
only they have an extra timezone argument:

    struct tm *	localtime_z(const time_t *, struct tm *, const timezone_t);
    char *		ctime_z(const time_t *, char *, const timezone_t);
    time_t		timelocal_z(struct tm *, const timezone_t);
    time_t		mktime_z(struct tm *, const timezone_t);
    time_t		time2posix_z(time_t, const timezone_t);
    time_t		posix2time_z(time_t, const timezone_t);

The changes to the source are minimal (the diffs are slightly larger
because I made things use ansi prototypes and removed 'register '.
I don't care about the names or the signatures much, just something
I came up as a proof of concept. Here's example code:

    #include "timeextra.h"
    #include <stdlib.h>
    #include <stdio.h>

    int
    main(int argc, char *argv[])
    {
	    size_t i;
	    char buf[60];
	    time_t t = time(NULL);
	    timezone_t *tz = malloc(argc * sizeof(*tz));
	    for (i = 1; i < argc; i++) {
		    tz[i] = tzalloc(argv[i]);
		    if (tz[i] == NULL)
			    err(1, "Cannot find timezone %s", argv[i]);
	    }
	    for (i = 1; i < argc; i++) {
		    printf("[%s] [%s] %s", tzgetname(tz[i], 0),
			tzgetname(tz[i], 1),
			ctime_z(&t, buf, tz[i]));
		    tzfree(tz[i]);
	    }
	    return 0;
    }

Has anyone done this work or similar?
Do you think others might want something like this?
Are you interested in taking a look at the changes/incorporating them?
Do you have any other suggestions?

Best Regards,

christos

Olson, Arthur David (NIH/NCI) [E]

lennox＠cs.columbia.edu

Ian Abbott

Ian Abbott

christos＠zoulas.com

Garrett Wollman

Eric Fischer

christos＠zoulas.com

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