> not to spark a debate Although the majority of this thread is as clear as mud, it is still interesting, even for simple VBA programmers like me that have no chance (maybe via a VB6 ActiveX exe) to use multi-threading.
RBS > Emerson, one posts to a forum like this to get help and other ideas, not > to spark a debate. Many talented people gave you some of their time to > help you solve your problem and one in particular gave you a well > conceived and executed piece of software free of charge. Appreciate > their charity. > > If you have some insights which have escaped the rest of us, implement > them and present the results to the world and dazzle us. > > BTW, a major advantage of Open Source software is that you do not need > to have people explain it to you. You have the source and that explains > everything. That is particularly so with Sqlite, which is clearly > written and consequently the source reads like a book. A few minutes > with the source and grep and you have your answers. > > Emerson Clarke wrote: >> John, >> >> Um, alright then... >> >> But i think your preaching to the converted, simplifying things is >> what i always try to do. And not just when theres a problem.... >> >> If you followed the thread fully you would realise that there was >> never a problem with my design, though that didnt stop many people >> from chirping in and offering suggestions. >> >> The problem i had was with sqlite not being compatible with the simple >> design that i wanted. I did try several alternate designs, but only >> as a way of working around the problem i had with sqlite. It took a >> long time but eventually i managed to get someone to explain why >> sqlite had that particular problem, and i was able to modify the >> sqlite source to resolve the issue. >> >> Unfortunately no one has yet commented on my solution, or the problem >> which it addresses. Basically sqlite has thread safety checking >> routines which work a little like mutexe's. Every time you enter a >> bit of code which is potentially thread unsafe it sets a magic number, >> then resets it when it comes out. This is an attempt to detect when >> two threads are accessing the same bit of code at the same time. >> >> Clearly its not 100% reliable, and is subject to all kinds of thread >> races, but it does provide some measure of protection. Unfortunately >> though, the way it has been coded, an unbalanced safety check is >> performed in the sqlite3_step() function. >> >> This is equivalent to entering a mutex but never leaving, which causes >> deadlock in a multithreaded program. Only in this situation sqlite >> throws a misuse error any time two or more threads use sqlite3_step() >> at the same time, even if those threads are synchronised and perfectly >> safe. >> >> The easy solution is to disable the safety checks, the propper >> solution is to balance out the checks in sqlite3_step() so that users >> who actually wish to use sqlite in a multithreaded program are free to >> synchronise access to the api without error and there is still a >> reasonable level of safety checking for users who do not synchronise >> properly. >> >> >> Emerson >> >> On 1/5/07, John Stanton <[EMAIL PROTECTED]> wrote: >> >>> Work on turning "reasonable" into "adequate" or "good" and it will help >>> you get an intuitive feel for the design of programs such as yours. >>> Then your programs will be simple, fast and robust, as Einstein >>> counselled - "Make it as simple a possible, but no simpler". >>> >>> I also suggest that you take Niklaus Wirth's advice and when you run >>> into a difficulty backtrack your work and scrap everything until you >>> reach a point where there are no problems and start again from that >>> point taking a different approach having learned a lesson from your >>> previous attempt. >>> >>> By the way, I doubt whether you are using a modern operating system, it >>> is most likely to be old technology like Windows or Linux. Neither >>> supports much in the way of parallelism. >>> >> >> ----------------------------------------------------------------------------- >> >> To unsubscribe, send email to [EMAIL PROTECTED] >> ----------------------------------------------------------------------------- >> >> > > > ----------------------------------------------------------------------------- > To unsubscribe, send email to [EMAIL PROTECTED] > ----------------------------------------------------------------------------- > > > ----------------------------------------------------------------------------- To unsubscribe, send email to [EMAIL PROTECTED] -----------------------------------------------------------------------------
