I felt difficulties in writing multithreading communication program more in Linux than in Windows. Especially the following two categories of APIs are less intuitive than those of Windows.
- Low level file I/O like open, close, read, write; Similar to Windows CreateFile, ReadFile, etc.
- Signal APIs like sigaction and related timer APIs; Similar to Windows event and TimerQueueTimer
Therefore I tried to design a small test program utilizing following components,
- Interval timer,
- Timer event dispatcher, and
- Low level blocking file I/O for serialports.
The sequence diagram is shown below.
Participants in the diagram are:
- IntervalTimer : Linux system timer set by setitimer(ITIMER_REAL,) to generate SIGALRM at each 10 ms.
- TimerEventDispatcher1 : A down counter and a callback function; send a string at each second.
- TimerEventDispatcher2 : Down counter and callback function; send SIGINT to the read thread.
- ReadThread : repeatedly call read() function.
Releted APIs
- settimer : setup an interval timer generating SIGALRM signal
- sigaction : set a signal handler
It is driven by the interval timer described above. Each dispatcher consists of
- downcounter : giving the first timeout,
- reload register : giving period of periodical timeout,
- callback function : called at each timeout
- parameter of the callback function
- mutex
Serialport settings are complicated and I studied detailed technique by
I carefully read Linux man pages and signal.h header file. Man pages, settimer, sigaction were useful.
It was not easy to understand the contents of the man pages and I have not yet well understood.
- app : test apps main code
- base : base library functions
- docs : documents
They are built with Makefile in the project root directory. Run make as follows.
> make all
The executables are created in debug/bin/ and release/bin/.