Mint_21.3 drawing-area和goocanvas的FB笔记(三)

一、改变goocanvas线条自动画线时间间隔

通过系统SIGALRM信号触发，每秒画一条线对于慢温湿度等慢变信号可以应付，但对于快速信号1秒的间隔就太慢了。可以改变方式，通过另外的线程，完成要做的任务。

1. 线程的回调函数 myfunc

2. 循环运行的线程函数 threadtimer

3. 创建线程，无需等待线程结束

4. 进入主程循环

#include once "glib.bi"

'Thread callback
Function myfunc Cdecl (Byval NotUsed As Any Ptr) as guint
	Print "Main-program time = ", Time$
	Return TRUE
End Function

'Thread endless loop
Function threadtimer(ByVal invalue as Integer) as integer
	Do while inkey$<> CHR$(27)
		Sleep 200
		Print "Thead-process time = ", Time$
		myfunc(NULL)
	Loop
	Return TRUE
End function

'Create thread
Dim as any ptr threadid = threadcreate( CAST(Any Ptr, @threadtimer), 0 )

'Main loop
'Press ESC to terminate
Do while inkey$<>chr$(27)
	Sleep 100
Loop

End

执行结果：

FreeBasic是多线程的，根据需要还可以创建更多线程，线程循环中sleep 200改为 sleep 100 则线程任务被执行的频率就会更高。

二、让SIGALRM为线程提供安全保护

上面的线程是个死循环，如果主程序很长，任务很重等其它原因死掉了，线程应该自动退出、让出系统资源。让SIGALRM做此事情即可解决这一问题。

系统在正常运行时，SIGALRM应该是长活的，如同C#中的系统线程池，它不是由用户创建的。它可以自动更新共享变量，在线程循环中对变量更新进行判断，如果SIGALRM在更新共享变量，则清FlagSet, 否则自动累加，这样如果因程序死掉了而不能更新共享变量的话，线程应该也就因此自动结束了。

三、可以使用线程锁

如果线程读写变得复杂，可以对变量或过程读写加锁，freebasic 支持 mutexlock 和 mutexunlock。

#include once "glib.bi"

const SIGALRM=14
Dim shared as Integer FlagSet = 0
Dim shared as Integer FlagCounterNew = 0
Dim shared as Integer FlagCounterOld = 0

Dim shared as any ptr maintlock, threadlock
Dim as any ptr threadid

Declare Function Signal cdecl  alias "signal" (ByVal V_Signal As long, byval V_Function As Any Ptr) as Any Ptr
Declare Function Raise cdecl  alias "raise" (ByVal V_Signal As long) as Any Ptr
Declare function alarm cdecl alias "alarm" (byval __seconds as uinteger) as uinteger

mainlock = mutexcreate( )
threadlock = mutexcreate( )

'Thread callback
Function myfunc Cdecl (Byval NotUsed As Any Ptr) as guint
	Print "Main-program time = ", Time$
	Return TRUE
End Function

'Thread endless loop
Function threadtimer(ByVal invalue as Integer) as integer
	Do while inkey$<> CHR$(27)
        Mutexlock threadlock
        If FlagCounterNew <> FlagCounterOld then
            FlagSet = 0
            FlagCounterOld = FlagCounterNew
        Else
            FlagSet += 1
            If FlagSet > 20 then
                FlagSet = 0
                Exit Do
            End if
        End if
        MutexUnlock threadlock
		Sleep 200
		Print "Thead-process time = ", Time$
		myfunc(NULL)
	Loop
	Return TRUE
End function

Sub timerevent()
    MutexLock mainlock
	FlagCounterNew += 1
    If FlagCounterNew > 1000 then
        FlagCounterNew = 0
    End if
    MutexUnlock mainlock
End Sub

sub wait_alarm(iSigno As Integer)
	'?"This is the scheduled event SIG = " & Str$(iSigno) & "--- @: " & Time$
	alarm(1)		'loads another alarm events: each alarm event is a single time event, so to repeat it it must be set again every time
	timerevent
end sub

signal(SIGALRM, @wait_alarm)		'when SIGALRM triggered, call subroutine wait_alarm
alarm(2)	

'Create thread
threadid = threadcreate( CAST(Any Ptr, @threadtimer), 0 )

'Main loop
'Press ESC to terminate
Do while inkey$<>chr$(27)
	Sleep 100
Loop

End

如果是gtk界面程序，可以简单地使用g_timeout_add(100, @myfunc, NULL) 完成100毫秒间隔的回调函数执行，直到回调函数返回FALSE结束。

#INCLUDE once gtk/gtk.h
#DEFINE __USE_GTK3__

'Thread callback
Function myfunc Cdecl (Byval NotUsed As Any Ptr) as guint
Print "Callback time = ", Time$
Return TRUE
End Function

gtk_init(NULL, NULL)
g_timeout_add(100, @myfunc, NULL)
gtk_main()

如果还有一个回调任务要完成，则加多一行任务，比如：

g_timeout_add(100, @myfunc1, NULL)

g_timeout_add(100, @myfunc2, NULL)

可直接编译运行的实测代码：

#DEFINE __USE_GTK3__
#Include once "gtk/gtk.bi"

Declare Function myfunc Cdecl (Byval NotUsed As Any Ptr) as guint

'Thread callback
Function myfunc Cdecl (Byval NotUsed As Any Ptr) as guint
	Print "Callback time = ", Time$
	Return TRUE
End Function

gtk_init(NULL, NULL)
var mycall = g_timeout_add (100, @myfunc, NULL)
gtk_main()

上面的代码测试了Timer, 但主程序只能等待gtk_main()结束才能继续。如果将gtk这段代码作为一个线程运行，而且主程序不等待线程结束的话，则线程运行的同时主程序仍然继续运行。

测试代代码改写为：

#DEFINE __USE_GTK3__
#Include once "gtk/gtk.bi"

Declare Function myfunc Cdecl (Byval NotUsed As Any Ptr) as guint

'Thread callback
Function myfunc Cdecl (Byval NotUsed As Any Ptr) as guint
	Print "Callback time = ", Time$
	Return TRUE
End Function

Sub sidethread()
	gtk_init(NULL, NULL)
	var mycall = g_timeout_add (300, @myfunc, NULL)
	gtk_main()
End Sub

Dim as any ptr threadid = threadcreate( CAST(Any Ptr, @sidethread), 0 )

''Main loop
Do while inkey$<>chr$(27)
	Print "Main program time = ", Time$
	Sleep 100
Loop

End 0

Gnu 对 glib 描述有一段文字()： Libraries may contain wrappers of some of these functions, e.g. gtk_main(), gtk_main_quit() and gtk_events_pending().

是说gtk_main()， gtk_main_quit，gtk_events_pending() 是 g_main_xxx 的封装 (wrapper) --- (Gnu 站点链接贴图本意只是为了不在CSDN外链)。上面的测试程序引用了 gtk，下面的测试程序使用glib验证了同样的效果。

#Include once "glib.bi"

Declare Function myfunc Cdecl (Byval NotUsed As Any Ptr) as guint

'Thread callback
Function myfunc Cdecl (Byval NotUsed As Any Ptr) as guint
	Print "Callback time = ", Time$
	Return TRUE
End Function

Dim shared as GMainLoop PTR gml = NULL
Sub sidethread()
	gml = g_main_loop_new(NULL, FALSE)
	var mycall = g_timeout_add (300, @myfunc, NULL)
	g_main_loop_run(gml)
    g_main_loop_unref(gml)
End Sub

Dim as any ptr threadid = threadcreate( CAST(Any Ptr, @sidethread), 0 )

''Main loop
Do while inkey$<>chr$(27)
	Print "Main program time = ", Time$
	Sleep 100
Loop

'When main program terminate, all thread should be removed off
'but, anyway, g_main_loop_quit(gml) is not harm to added here
g_main_loop_quit(gml)
End 0