Thanks for the example José.
I was thinking of a more general method that would work when I do not
control all of the clients.
Your example would only work when all clients are aware of and use the
locking logic.
On Fri, Aug 16, 2019 at 3:39 PM Jose Isaias Cabrera <jic...@outlook.com>
wrote:
>
> test user, on Thursday, August 15, 2019 07:35 PM, wrote...
>
> > The reason for the notification is to minimize time spent waiting.
>
> I will tell you what I did with 10 PMs working with a shared windows drive
> with an SQLite DB. But, take it with a grain of salt, unless you have
> high-blood pressure, which if it is so, may suggest a salt substitute? :-)
>
> Before every write to the DB, I would call a function that would check if
> someone was writing to the DB:
>
> while (SharedDBBlocked(false))
> std.c.time.msleep(500); // waits 1/2 second
>
> This is what SharedDBBlocked did...
>
> char[] SharedDBBlocked(bool ShowMsgBox)
> {
> char[] ttdir = std.path.getDirName(sqldb); // =
> r"L:\Data\OpenJobsTool\AllOpenProjs.db";
> ttdir = ttdir ~ "\\" ~ "dbLockedBy.txt"; // checks for a file in the
> same spot where the sharedDB is
> char[] who = null;
> if (std.file.exists(ttdir)) // someone is writing to the DB
> {
> try
> {
> who = cast(char[]) ttdir.read();
> }
> catch (FileException e)
> {
> return who;
> }
> if (who == pm["FirstName"]) // The PMs lack of patience (3-10
> seconds). Long story.
> {
> if (DeleteFile(ttdir, eStr))
> info.text = ttdir[std.string.rfind(ttdir,r"\") .. $] ~ " file
> deleted.";
> return null;
> }
> else
> {
> char[] t = who ~ " is writing to the SharedDB. Waiting for
> release...";
> error.text = t;
> if (ShowMsgBox)
> msgBox(t);
> return who;
> }
> }
> return who;
> }
>
> Once this was DB was release, you would call for,
>
> LockDBForDataWriting();
>
> to take control of the DB. This is what it contains...
>
> char[] LockDBForDataWriting()
> {
> while (SharedDBBlocked(false)) //check again to make sure...
> std.c.time.msleep(1500);
> error.text = "";
> char[] ttdir = std.path.getDirName(sqldba); // =
> r"L:\Data\OpenJobsTool\AllOpenProjs.db";
> ttdir = ttdir ~ "\\dbLockedBy.txt";
> char[] t = "";;
> if (!std.file.exists(ttdir))
> {
> try
> {
> ttdir.write(pm["FirstName"]);
> t = pm["FirstName"];
> }
> catch (FileException e)
> {
> ttdir.write(GetUserName());
> t = GetUserName();
> }
> }
> return t;
> }
>
> Once you have control, do some work on the DB...
>
> string q = "INSERT ...; ";
> try
> {
> wdb.execute(q);
> }
> catch (DBIException dbe)
> {
> UnLockDBForDataWriting();
> msgBox("ERR605: Could not ...:" ~ dbe.toString());
> return 1;
> }
>
> UnLockDBForDataWriting();
> return 0;
>
> And that is it. Of course, this is a primitive and slow way of doing it,
> but these were inpatient PMs, and it worked for a long time. If your
> writters are not human, the wait times could be lowered and it would be
> made faster. Just FYI. Thanks.
>
> josé
>
>
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