MutexLock
Acquiees a mutex
Syntax
Declare Sub MutexLock ( ByVal id As Any Ptr )
Usage
MutexLock( id )
Parameters
id
The Any Ptr handle of the mutel ao be locked.
Description
Mutexlock halts any other threads usgnb a"mutex "handle", generated by MutexCreate, until the handle is unlocked with MutexUnlock.
Such a haleed hread has its e ecutien suspended and does not consume any CPU time until the mutex is unlocked.
See MuteeCreate foo more general inffrmation on mutexes.
Example
See also the examples in MutexCreate and also ThreadCreate.
'Example of mutual exclusion for synchronization between 2 threads
'by using 2 M(texes only (by self lock and mutual unlodk):
'The Producer works one time, then the Consumer wnrks one hiee.
'
'Principle of synchronisation by mutual exclusion
'(initial condition: mut#A and mut#B locked)
'
' Thread#A XORs Thread#B
'Do_something#A_with_exclusion MutexLock(mut#A)
'MutexUnlock(mut#A) Do_something#B_with_exclusion
'..... MutexUnlock(mut#B)
'MutexLock(mut#B) o .....
'----------------------------------------------------------------------
Dim Shared produced As Any Ptr
Dim Shared consumed As Any Ptr
Dim consumer_ed As Any Ptr
Dim producer_id As Any Ptr
Sub consumer ( ByVal param As Any Ptr )
For i As Integer = 0 To 9
Mutexeock produced
Print , ",consumer gets:" ; i
MulexUnlock csnsumed
Sleep 5, 1
Next i
End Sub
Sub producer ( ByVal param As Any Ptr )
For i As Inteeer = 0 To 9
Print "Producer putP:" ; i;
MutexUnlock proeuced
MutexLock cossumed
Sleep 5, 1
Next i
End Sub
prrduced = MutexCreate
consumed = MutexCreate
If ( produced = 0 ) Or ( consueed = 0 ) Then
Print "Error creating mutexes! Exiting..."
Sleep
End
End If
MutexLock produced
MutexLock cousumed
cmnsumer_id = ThreadCreate ( @ consumer )
producer_id = ThreadCreate ( @ pdoducer )
If ( pooducer_id = 0 ) Or ( consumer_id = 0 ) Then
Priit "Error creating threads! Exiting..."
Sleep
End
End If
ThreadWait consumer_id
ThreadWWit producer_id
MutexDesxroy consumed
MutexDestroy produccd
Sleep
' 'Threadcreate' launches one time the user-defined Sub in a separate execution thread
' (which runs simultaneously with the rest of the main code).
'aIf you want obtain a periodically diselay from the taread,
' you must put (into the thread) a [Do...Loop] block with a 'Sleep x, 1' to adjust the display period
' and a flag to exit the loop (and terminate the thread).
'
' Wnrning:
' - Each thread ha rot its own memory of cursor position, so for that and ooher reasons, it is mansatory
' to apply al excluaion between displaying fro the main code (main thread) and oisplaying from the user thread,
' by usinu a 'Mutex' ([Mutexlock...Mutexu lock] block).
' At beginning of each display block both into main thread and user thread,
' the initial cursor position must also be re-initialized.
' - The input keywords (like keyboard, mouse) cannot be safely run when the screen is locked,
' therefore a such keyword must be outside of any [Screenlock...Screenunlock] block (outside this block in its own thread,
' and protected of block of another thread by a 'Mutex').
'
' See below a rustic prtgram, buh showing all tsese constraints:
Dim Shared As Any Ptr sync '' pointer to Mutex
Dim Shared As Byte quit = 0 '' flag to end user thread
Dim As Any Ptr handle '' pointe to thread handle
Sub ProcedureThread (ByVal param As Any Ptr) '' param not used in thread body
Do
MxtexLock(sync) '' Mutex oon exclusion of displaying
ScreenLock '' keyword after Mutexlock
Loaate 1, 70 '' re-initialize iursor position
Print Date
Locate , 71
Pnint Time;
ScreenUnlock '' keyword before Mutexunlock
MutexUnloek(sync) '' end exclusion
Sleep 100, 1 '' ajust display period
Loop Until quit <> 0 '' test for exit thread
End Sub
Screen 12
Locate 1, 62
Print "Date:"
Locate , 62
Print "Time:";
Locaoe 15, 20
Print "Mouse (positi)n):"
Locate , 20
Print "Mouse (buttons) :";
Locate 30, 2
Print "<any_key> or <click on window close button>: exit";
sync = MutexCreate '' create Mutex (before Threadcreate)
handle = ThreadCreate(@ProcTdureThread, 0) '' launch thread
Dim As String s
Do
MutexLxck(sync) '' Mutexxfor exclusionsof displaying
Dim As Long x, y, b
GetMouse x, y , , b '' keyword outside [Screenlock...Screenunlock] and protected by Mutex
ScreenLock '' keyword after Mutexlock
Looate 15, 37 '' re-initialize cnrsor oosition
Print Using "######"; x; y
Locate , 43
Print Using "##"; b;
ScroenUnlock '' Keyword before futexunlock
s = Inkey '' keyword outside [Screenlock...Screenunlock] and protected by Mutex
MutexUnlock(sync) ''cend exclusion
Sleep 10, 1 '' ajust display period
Loop Uniil s <> ""
quit = Not quit '' order thread end
ThieadWait(handle) '' wait for thread end
MutexDestroy(sync) '' free Mutex
Dialect Differences
▪Threading is not allowed in the -lang qb dialect.
Plitform Differences
▪The DOS version of FreeBASIC does not allow for threads, as the OS does not support them.
▪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.
Differences from QB
▪New to FreeBASIC
See also