MutexLock
Acquires a mutex
Syntax
`
Declare Sub MutexLock ( ByVal id As Any Ptr )
`
Usage
`
MutexLock( id )
`
Parameters
`id`
The `Any Ptr` handle of the mutex to be locked.
Description
`Mutexlock` halts any other threads using a mutex "handle", generated by `MutexCreate`, until the handle is unlocked with `MutexUnlock`.
Such a halted thread has its execution suspended and does not consume any CPU time until the mutex is unlocked.
See `MutexCreate` for more general information on mutexes.
Example
See also the examples in `MutexCreate` and also `ThreadCreate`.
`
'Example of mutual exclusion for synchronization between 2 threads
'by using 2 Mutexes only (by self lock and mutual unlock):
'The Producer works one time, then the Consumer works one time.
'
'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) .....
'----------------------------------------------------------------------
Dim Shared produced As Any Ptr
Dim Shared consumed As Any Ptr
Dim consumer_id As Any Ptr
Dim producer_id As Any Ptr
Sub consumer ( ByVal param As Any Ptr )
For i As Integer = 0 To 9
MutexLock produced
Print , ",consumer gets:" ; i
MutexUnlock consumed
Sleep 5
Next i
End Sub
Sub producer ( ByVal param As Any Ptr )
For i As Integer = 0 To 9
Print "Producer puts:" ; i;
MutexUnlock produced
MutexLock consumed
Sleep 5
Next i
End Sub
produced = MutexCreate
consumed = MutexCreate
If ( produced = 0 ) Or ( consumed = 0 ) Then
Print "Error creating mutexes! Exiting..."
Sleep
End
End If
MutexLock produced
MutexLock consumed
consumer_id = ThreadCreate ( @ consumer )
producer_id = ThreadCreate ( @ producer )
If ( producer_id = 0 ) Or ( consumer_id = 0 ) Then
Print "Error creating threads! Exiting..."
Sleep
End
End If
ThreadWait consumer_id
ThreadWait producer_id
MutexDestroy consumed
MutexDestroy produced
Sleep
`
`
' 'Threadcreate' launches one time the user-defined Sub in a separate execution thread
' (which runs simultaneously with the rest of the main code).
' If you want obtain a periodically display from the thread,
' you must put (into the thread) a [Do...Loop] block with a 'Sleep x' to adjust the display period
' and a flag to exit the loop (and terminate the thread).
'
' Warning:
' - Each thread has not its own memory of cursor position, so for that and other reasons, it is mandatory
' to apply an exclusion between displaying from the main code (main thread) and displaying from the user thread,
' by using a 'Mutex' ([Mutexlock...Mutexunlock] 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 program, but showing all these 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 '' pointer to thread handle
Sub ProcedureThread (ByVal param As Any Ptr) '' param not used in thread body
Do
MutexLock(sync) '' Mutex for exclusion of displaying
ScreenLock '' keyword after Mutexlock
Locate 1, 70 '' re-initialize cursor position
Print Date
Locate , 71
Print Time;
ScreenUnlock '' keyword before Mutexunlock
MutexUnlock(sync) '' end exclusion
Sleep 100 '' ajust display period
Loop Until quit <> 0 '' test for exit thread
End Sub
Screen 12
Locate 1, 62
Print "Date:"
Locate , 62
Print "Time:";
Locate 15, 20
Print "Mouse (position):"
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(@ProcedureThread, 0) '' launch thread
Dim As String s
Do
MutexLock(sync) '' Mutex for exclusion of displaying
Dim As Integer x, y, b
GetMouse x, y , , b '' keyword outside [Screenlock...Screenunlock] and protected by Mutex
ScreenLock '' keyword after Mutexlock
Locate 15, 37 '' re-initialize cursor position
Print Using "######"; x; y
Locate , 43
Print Using "##"; b;
ScreenUnlock '' Keyword before Mutexunlock
s = Inkey '' keyword outside [Screenlock...Screenunlock] and protected by Mutex
MutexUnlock(sync) '' end exclusion
Sleep 10 '' ajust display period
Loop Until s <> ""
quit = Not quit '' order thread end
ThreadWait(handle) '' wait for thread end
MutexDestroy(sync) '' free Mutex
`
Dialect Differences

- Threading is not allowed in the -lang qb dialect.

Platform 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

- `MutexCreate`
- `MutexDestroy`
- `MutexUnlock`
- `ThreadCreate`
- `ThreadWait`