By Thang Nguyen
Currently, my vision software will do a compression (subtract to background image then count zero) and write to a table in SQLite file. Since we want to speed up the process, I write entire image in a temporary table. Then at the end, I read the table, do compression and write to the actual table, then drop the temporary table. This takes a lot of time too even I use the Journal mode = memory. I think the issue is I put the process code in 4 separated modules:
Select the temp table -> output array Compress the output array of step 1 Insert the compress data from step 2 to actual table Drop the temp table I am looking for an option to mix these steps together to speed up the speed for example select and delete the row in temp table at the same time then at the end I can drop the table faster. Currently, it takes significant time to drop the table. Our raw data can be up to 3GB. But I don't know how to combine the query. I also read that SQlite does not support this. So I also looking for an advice on how to make this process more efficient. I thought about using the queue too but I need input before I change it.
Thank you in advance.
Hello, I wrote a LabVIEW program to communicate with a hardware sensor using vendor-provided LLB and a DLL files. The program runs fine on my workstation both from LabVIEW IDE and from a compiled executable. The problem starts when I copy the entire executable folder to a target host without a LabVIEW IDE (only with a runtime engine). The application opens with a broken Run arrow and a "missing external function" error message appears for every function call I made to the DLL (see attached).
I have tested my application on 5 completely different Windows 10 computers managed by different people. On three of them with various versions of LabVIEW IDE my executable opened with a whole Run arrow and no error message. Two other machines previously had no LabVIEW, so I installed a Runtime Engine 2017f2 32-bit with default settings to match the version of my IDE. Both gave an identical error message.
The DLL is always included in the application build. I have tried placing the DLL in every conceivable location on the target host: in the executable folder, in the /data folder, in the c:\Windows and system32 folders... I even created a full folder tree matching the location of the project on the developer workstation. Same error. When I intentionally hide the DLL, my executable prompts me to point to it upon being opened, and when I do, I get all the same error messages.
Vendor documentation only asks to put the two files in the same folder. From programmer's manual: " The driver was written in LabWindows/CVI, version 4.0.1 and is contained in a dynamic link library which can be linked with a variety of programming languages." There is no vendor-provided support.
One way I actually got rid of the error message was by editing every Call Library Function Node in every VI in the LLB to use relative path to DLL together with the Application Directory VI. However, I feel that there has got to be a better way to compile than by editing a vendor-provided library, especially since it works as-is on some computers. Can anyone suggest what it is?
Thank you for your time!
I (re)watched James Powell's talk at GDevCon#2 about Application Design Around SQLite. I really like this idea as I have an application with lots of data (from serial devices and software configuration) that's all needed in several areas of the application (and external applications) and his talk was a 'light-bulb' moment where I thought I could have a centralized SQLite database that all the modules could access to select / update data.
He said the database could be the 'model' in the model-view-controller design pattern because the database is very fast. So you can collect data in one actor and publish it directly to the DB, and have another actor read the data directly from the DB, with a benefit of having another application being able to view the data.
Link to James' talk: https://www.youtube.com/watch?v=i4_l-UuWtPY&t=1241s)
I created a basic proof of concept which launches N-processes to generate-data (publish to database) and others to act as a UI (read data from database and update configuration settings in the DB (like set-point)). However after launching a couple of processes I ran into 'Database is locked (error 5) ', and I realized 2 things, SQLite databases aren't magically able to have n-concurrent readers/writers , and I'm not using them right...(I hope).
I've created a schematic (attached) to show what I did in the PoC (that was getting 'Database is locked (error 5)' errors).
I'm a solo-developer (and SQLite first-timer*) and would really appreciate it if someone could look over the schematic and give me guidance on how it should be done. There's a lot more to the actual application, but I think once I understand the limitations of the DB I'll be able to work with it.
*I've done SQL training courses.
In the actual application, the UI and business logic are on two completely separate branches (I only connected them to a single actor for the PoC)
Some general questions / thoughts I had:
Is the SQLite based application design something worth perusing / is it a sensible design choice? Instead of creating lots of tables (when I launch the actors) should I instead make separate databases? - to reduce the number of requests per DB? (I shouldn't think so... but worth asking) When generating data, I'm using UPDATE to change a single row in a table (current value), I'm then reading that single row in other areas of code. (Then if logging is needed, I create a trigger to copy the data to a separate table) Would it be better if I INSERT data and have the other modules read the max RowId for the current value and periodically delete rows? The more clones I had, the slower the UI seemed to update (should have been 10 times/second, but reduced to updating every 3 seconds). I was under the impression that you can do thousands of transactions per second, so I think I'm querying the DB inefficiently. The two main reasons why I like the database approach are:
External applications will need to 'tap-into' the data, if they could get to it via an SQL query - that would be ideal. Data-logging is a big part of the application. Any advice you can give would be much appreciated.
(I'm using quite a few reuse libraries so I can't easily share the code, however, if it would be beneficial, I could re-work the PoC to just use 'Core-LabVIEW' and James Powell's SQLite API)
DLL functions or shared variables? Or something else?
I have a Labview 2014-64 executable (or I can build a DLL) that runs one piece of equipment, the X-ray. The other engineer has a large CVI Labwindows 2015 + MS Visual Studio 2012 (C++) executable that runs everything else. I want the Labview code to be a slave of the CVI code, accepting commands to turn X-ray On or Off, reporting failures, and the like. Translating the X-ray code into C++ would be possible in principle, but not fun.
Shared variables look easy, but I'm kinda scared of them. I would define all the shared variables in my LV code, since I'm more familiar with LV, then use them in both. There's a thread in here called "Shared Variable Woes" so maybe I should be scared. In the alternative, I tried building a proof-of-concept DLL in Labview, and calling its functions in CVI/C++, and it works, but it's kinda clunky. (I'm attaching it below in case you want to play, or advise.)
Your advice would be appreciated.
To use a controller from LabVIEW I have to use some functions of a DLL.
For one of the functions, according to the header file .h there is a structure data with parameters of different types that I have to pass to the dll. Some of the parameres are BYTE (1 Byte) and WORD (2 Bytes).
When compiling this kind of structure with Visual C++ and looking at it's size with "sizeof()" it seems to me that 4 Bytes variables have to start in a position multiple of 4. For example if there is a BYTE and then a DWORD, the 3 Bytes after the BYTE are ignored and the DWORD starts at Bytes 5 to 8.
When defining a LabVIEW cluster to match the DLL structure, will LabVIEW do the same? If in my cluster there is a U8 variable and then a U32, will anyway the U8 take 4 bytes?