Creare un Timer con le funzioni esterne delle librerie standard C "signal.h" e "time.h"

Usando alcune funzioni esterne delle librerie standard C "signal.h" e "time.h", è possibile creare ed utilizzare un Timer

E' necessario avere installata nel sistema e richiamare in Gambas la libreria dinamica condivisa: "/usr/lib/vlc/plugins/access/libtimecode_plugin.so"

Mostriamo un esempio:

Private id As Long
Private num As Byte
 

Library "libc:6"

Private Const SIGALRM As Integer = 14      ' Alarm clock (POSIX)

' __sighandler_t signal (int __sig, __sighandler_t __handler)
' Set the handler for the signal SIG to HANDLER.
Private Extern signal(__sig As Integer, __handler As Pointer) As Pointer


Library "/usr/lib/vlc/plugins/access/libtimecode_plugin"

Public Struct timespec
  tv_sec As Long
  tv_nsec As Long
End Struct

Public Struct itimerspec
  it_interval As Struct Timespec
  it_value As Struct Timespec
End Struct

Private Enum CLOCK_REALTIME = 0, CLOCK_MONOTONIC, CLOCK_PROCESS_CPUTIME_ID, CLOCK_THREAD_CPUTIME_ID, CLOCK_MONOTONIC_RAW,
             CLOCK_REALTIME_COARSE, CLOCK_MONOTONIC_COARSE, CLOCK_BOOTTIME, CLOCK_REALTIME_ALARM, CLOCK_BOOTTIME_ALARM

' int timer_create (clockid_t __clock_id, struct sigevent *__restrict __evp, timer_t *__restrict __timerid)
' Create new per-process timer using CLOCK_ID.
Private Extern timer_create(__clock_id As Integer, __evp As Pointer, __timerid As Pointer) As Integer

' int timer_settime (timer_t __timerid, int __flags, const struct itimerspec *__restrict __value, struct itimerspec *__restrict __ovalue)
' Set timer TIMERID to VALUE, returning old value in OVALUE.
Private Extern timer_settime(__timerid As Long, __flags As Integer, __value As Itimerspec, __ovalue As Itimerspec) As Integer

' int timer_delete (timer_t __timerid)
' Delete timer TIMERID.
Private Extern timer_delete(__timerid As Long) As Integer


Public Sub Main()
  
  signal(SIGALRM, timer_callback)
  
  Start_Timer(300000000)
  
  While num < 99
    Sleep 0.01
  Wend
   
  Stop_Timer()
   
  timer_delete(id)
  
End


Private Procedure Start_Timer(vlr As Long)
 
 Dim spec As New Itimerspec
   
  With spec
    .it_value.tv_sec = 0
    .it_value.tv_nsec = vlr     ' Attende 300.000.000 di nanosecondi prima di inviare un segnale Timer
    .it_interval.tv_sec = 0
    .it_interval.tv_nsec = vlr  ' Invia un segnale Timer ogni 300.000.000 nanosecondi
  End With
  
  timer_create(CLOCK_REALTIME, 0, VarPtr(id))
  timer_settime(id, 0, spec, Null)
 
End
 
  
Private Procedure timer_callback(signum As Integer)
 
 Print num; "   Intercettato segnale Timer: "; signum
 
 Inc num
 
End


Private Procedure Stop_Timer()
 
 Dim spec As New Itimerspec
   
  With spec
    .it_value.tv_sec = 0
    .it_value.tv_nsec = 0
    .it_interval.tv_sec = 0
    .it_interval.tv_nsec = 0
  End With
   
  timer_settime(id, 0, spec, Null)
  timer_delete(id)
   
End

Riferimenti

• http://man7.org/linux/man-pages/man2/timer_create.2.html
• http://pubs.opengroup.org/onlinepubs/009695399/functions/timer_create.html
• https://linux.die.net/man/2/timer_create
• http://www.gnu.org/software/libc/manual/html_node/Signal-Handling.html
• https://linux.die.net/man/2/signal
• http://digilander.libero.it/uzappi/C/librerie/funzioni/signal.html