{{fbdoc item="title" value="MUTEXLOCK"}}----
Acquires a mutex

{{fbdoc item="syntax"}}##
	[[KeyPgDeclare|declare]] [[KeyPgSub|sub]] **Mutexlock** ( [[KeyPgByval|byval]] //id// [[KeyPgAs|as]] [[KeyPgAny|any]] [[KeyPgPtr|ptr]] )
##
{{fbdoc item="usage"}}##
	**Mutexlock**( //id// )
##
{{fbdoc item="param"}}
	##//id//##
		The ##[[KeyPgAny|any]] [[KeyPgPtr|ptr]]## handle of the mutex to be locked.

{{fbdoc item="desc"}}
	##Mutexlock## halts any other threads using a mutex "handle", generated by ##[[KeyPgMutexCreate|Mutexcreate]]##, until the handle is unlocked with ##[[KeyPgMutexUnlock|Mutexunlock]]##.
	Such a halted thread has its execution suspended and does not consume any CPU time until the mutex is unlocked.
	
	See ##[[KeyPgMutexCreate|Mutexcreate]]## for more general information on mutexes.

{{fbdoc item="ex"}}
	See also the examples in ##[[KeyPgMutexCreate|Mutexcreate]]## and also ##[[KeyPgThreadCreate|Threadcreate]]##.

{{fbdoc item="filename" value="examples/manual/threads/mutexlock.bas"}}%%(freebasic)
'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
%%

{{fbdoc item="filename" value="examples/manual/threads/mutexlock2.bas"}}%%(freebasic)
' '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
%%

{{fbdoc item="lang"}}
	- Threading is not allowed in the //[[CompilerOptlang|-lang qb]]// dialect.

{{fbdoc item="target"}}
	- 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. 

{{fbdoc item="diff"}}
	- New to ""FreeBASIC""

{{fbdoc item="see"}}
	- ##[[KeyPgMutexCreate|Mutexcreate]]##
	- ##[[KeyPgMutexDestroy|Mutexdestroy]]##
	- ##[[KeyPgMutexUnlock|Mutexunlock]]##
	- ##[[KeyPgThreadCreate|Threadcreate]]##
	- ##[[KeyPgThreadWait|Threadwait]]##

{{fbdoc item="back" value="CatPgThreading|Threading Support Functions"}}