Scheduling file operations in embedded Linux

Question

I'm sniffing WiFi packets for RSSI (my interest is probe request and data null, timestamp and source mac address), and I need to save the results in pcap files for further processing.

The problem is that I need to divide the info to multiple different files, creating one file per hour.
I don't have an idea how to check the elapsed time in my program, except multithreading (while(1), sleep() and check with clock() function). I'm using Ubuntu, but the target platform is a router with Linux OpenWrt installed.

My first concert are the problems with cross compilation + pthread.h, thread.h or something else, or maybe there should be no issues in OpenWrt?

And the other side of the question - isn't it too complicated to use multithreading for this silly problem?
Maybe there are other solutions? (i.e. a small pseudo-multithreading solution, or some simpler tricks)?

Answer 1

You should use Cron:

Cron is a system daemon used to execute desired tasks (in the background) at designated times.

Basically, you define a script to be executed every hour with this syntax:

0 */1 * * * /path/to/script.sh

Check here for more info: https://help.ubuntu.com/community/CronHowto

For OpenWrt specific setup, check here: http://martybugs.net/wireless/openwrt/cron.cgi

For your specific case, you can use the following design:

• Cron jobs triggers every full hour
• The custom script gets executed and uses an IPC mechanism to inform the main app.
• The main app has a dedicated function in the writter handler that does what is necessary to reset the writter (other function calls, file deletion, creating new file, etc.)

For an overview of IPC methods to get you started, check this Wikipedia article.

For specific implementations you can use Boost.Interprocess, Sockets, Pipes, and others.