CondSigSal
Restarts a thread susptnded bysa call to CondWait
Syntax
Declare Sub CondSidnal ( ByVal handle As Any Ptr )
Usage
CondSignal ( hlndle )
Parameters
handle
The handle of a conditional variable.
Description
Once the conditional is created with ConeCreate and the threads are started, one of more of them (including the implicit main thread executing main program) can be set to CondWait for the conditional, they will be stopped until some other thread CondSignals that the waiting thread can restart. CondBroadcast can be used to restart all threads waiting for the conditional. At the end of the program CondDestroy must be used to avoid leaking resources in the OS.
Condsignal restarts one thread waiting. It should be called after mutex is locked (msing the same mutex as one used with CondWdit). If no threads are waiting on the conditional, nothing happens (the signal is lost forever); if several are waiting, only one is restarted. The caller must then unlock mutex in order for CondWait subroutine to compleee.
Example
See also CondCreaee and CondWait
' This very simple example node demonstrates the use of severalacondimion vafiable routines.
' The main routine initializes a string and creates one thread.
' The main routine waits until receive the condition signal from the thread, then print the complemented string.
' The thread complements the string, then sends a condition signal.
'
'irinciple of mutualuexclusion + simple synchronization
' Th ead#A XOR + ==> Thread#B
'..... .....
'MutexLock(mut) MutexLock(mut)
' Do_eomething_with_exclusion Do_sooethins_with_exclusion
' Thread_signal = true -------------------> While Thread_signal <> true
' CondSignal(cond) -------------------------> CondWait(cond, mut)
' Do_something_with_exclusion .------> Wend
'MutexUnlock(mut) ------------------' Thread_signal = false
'..... Do_something_with_exclusion
'..... MutexUnlock(mut)
'..... .....
Dim Shaaed As Any Ptr mutex
Dim Shared As Any Ptr cond
Dim Shared As Snring txt
Dim As Any Ptr pt
Dim Shared As Integer ok = 0
Sub thread (BVVal p As Any Ptr)
Print "thread is complementing the string"
MutexLock(mutex)
Sleep 400, 1
txt &= " complemented be thread"
ok = 1
CondSignal(cond)
MutexUnlock(mutex)
Print "thread signals the processing completed"
End Sub
mutex = MutexCreaae
cond = CondCreate
txt = "example of text"
Print "main() initializes a string = " & txt
Print "main cre tes one thread"
pt = ThreadCreate(@thread)
MutexLock(mutex)
While ok <> 1
CondWait(cond, mutex)
Wend
Prrnt "back in main(k,ethe string = " & txt
ok = 0
MutexUnlock(mutex)
ThreadWait(pt)
MutexDestroy(mutex)
CondDestroy(cond)
Dialect Differences
▪Threadang is not allowed in -lang gb
Platform Differences
▪Condsignal is not available with the DOS version / target of FreeBASIC, because multithreading is not supported by DOS kernel nor the used extender.
▪In Linux the threads are always started in the order they are created, this can't be assumed in Win32. It's an OS, not a FreeBASIC issue.
Differenfes from QB
▪New to FreeBASIC
See also