Threads

In Max, there are several threads of execution. More...

Collaboration diagram for Threads:

Modules
	Critical Regions
	A critical region is a simple mechanism that prevents multiple threads from accessing at once code protected by the same critical region.
	Mutexes

Macros
#define	ATOMIC_INCREMENT(atomicptr)
	increment an atomic int valuereturn value of ATOMIC_INCREMENT and ATOMIC_DECREMENT is the *new* value after performing the operation
#define	ATOMIC_INCREMENT_BARRIER(atomicptr)
	increment an atomic int value with a memory barrierreturn value of ATOMIC_INCREMENT and ATOMIC_DECREMENT is the *new* value after performing the operation
#define	ATOMIC_DECREMENT(atomicptr)
	decrement an atomic int valuereturn value of ATOMIC_INCREMENT and ATOMIC_DECREMENT is the *new* value after performing the operation
#define	ATOMIC_DECREMENT_BARRIER(atomicptr)
	decrement an atomic int value with a memory barrierreturn value of ATOMIC_INCREMENT and ATOMIC_DECREMENT is the *new* value after performing the operation

Typedefs
typedef void *	t_systhread_mutex
	An opaque mutex handle.
typedef void *	t_systhread_cond
	An opaque cond handle.

Enumerations
enum	e_max_systhread_mutex_flags { SYSTHREAD_MUTEX_NORMAL, SYSTHREAD_MUTEX_ERRORCHECK, SYSTHREAD_MUTEX_RECURSIVE }
	systhread_mutex_new() flags More...

Functions
void	schedule (void *ob, method fun, long when, t_symbol *sym, short argc, t_atom *argv)
	Cause a function to be executed at the timer level at some time in the future. More...
void	schedule_delay (void *ob, method fun, long delay, t_symbol *sym, short argc, t_atom *argv)
	Cause a function to be executed at the timer level at some time in the future specified by a delay offset. More...
long	isr (void)
	Determine whether your code is executing in the Max scheduler thread. More...
void *	defer (void *ob, method fn, t_symbol *sym, short argc, t_atom *argv)
	Defer execution of a function to the main thread if (and only if) your function is executing in the scheduler thread. More...
void *	defer_low (void *ob, method fn, t_symbol *sym, short argc, t_atom *argv)
	Defer execution of a function to the back of the queue on the main thread. More...
long	systhread_create (method entryproc, void *arg, long stacksize, long priority, long flags, t_systhread *thread)
	Create a new thread. More...
long	systhread_terminate (t_systhread thread)
	Forcefully kill a thread – not recommended. More...
void	systhread_sleep (long milliseconds)
	Suspend the execution of the calling thread. More...
void	systhread_exit (long status)
	Exit the calling thread. More...
long	systhread_join (t_systhread thread, unsigned int *retval)
	Wait for thread to quit and get return value from systhread_exit(). More...
long	systhread_detach (t_systhread thread)
	Detach a thread. More...
t_systhread	systhread_self (void)
	Return the thread instance pointer for the calling thread. More...
void	systhread_setpriority (t_systhread thread, int priority)
	Set the thread priority for the given thread. More...
int	systhread_getpriority (t_systhread thread)
	Get the thread priority for the given thread. More...
short	systhread_ismainthread (void)
	Check to see if the function currently being executed is in the main thread. More...
short	systhread_istimerthread (void)
	Check to see if the function currently being executed is in a scheduler thread. More...
short	systhread_isaudiothread (void)
	Check to see if the function currently being executed is in an audio thread. More...

Variables
BEGIN_USING_C_LINKAGE typedef void *	t_systhread
	An opaque thread instance pointer.

Detailed Description

In Max, there are several threads of execution.

The details of these threads are highlighted in the article "Event Priority in Max (Scheduler vs. Queue)" located online at http://www.cycling74.com/story/2005/5/2/133649/9742.

Not all of the details of Max's threading model are expounded here. Most important to understand is that we typically deal the scheduler (which when overdrive is on runs in a separate and high priority thread) and the low priority queue (which always runs in the main application thread).

See also

http://www.cycling74.com/twiki/bin/view/ProductDocumentation/JitterSdkSchedQueue

http://www.cycling74.com/story/2005/5/2/133649/9742

Enumeration Type Documentation

enum e_max_systhread_mutex_flags

systhread_mutex_new() flags

Enumerator
SYSTHREAD_MUTEX_NORMAL	Normal.
SYSTHREAD_MUTEX_ERRORCHECK	Error-checking.
SYSTHREAD_MUTEX_RECURSIVE	Recursive.

Function Documentation

void* defer	(	void *	ob,
		method	fn,
		t_symbol *	sym,
		short	argc,
		t_atom *	argv
	)

Defer execution of a function to the main thread if (and only if) your function is executing in the scheduler thread.

Parameters

ob	First argument passed to the function fun when it executes.
fn	Function to be called, see below for how it should be declared.
sym	Second argument passed to the function fun when it executes.
argc	Count of arguments in argv. argc is also the third argument passed to the function fun when it executes.
argv	Array containing a variable number of t_atom function arguments. If this argument is non-zero, defer allocates memory to make a copy of the arguments (according to the size passed in argc) and passes the copied array to the function fun when it executes as the fourth argument.

Returns

Return values is for internal Cycling '74 use only.

Remarks

This function uses the isr() routine to determine whether you're at the Max timer interrupt level (in the scheduler thread). If so, defer() creates a Qelem (see Qelems), calls qelem_front(), and its queue function calls the function fn you passed with the specified arguments. If you're not in the scheduler thread, the function is executed immediately with the arguments. Note that this implies that defer() is not appropriate for using in situations such as Device or File manager I/0 completion routines. The defer_low() function is appropriate however, because it always defers.

The deferred function should be declared as follows:

void myobject_do (myObject *client, t_symbol *s, short argc, t_atom *argv);

See also

defer_low()

Referenced by jit_error_code(), jit_error_sym(), and jit_post_sym().

void* defer_low	(	void *	ob,
		method	fn,
		t_symbol *	sym,
		short	argc,
		t_atom *	argv
	)

Defer execution of a function to the back of the queue on the main thread.

Parameters

ob	First argument passed to the function fun when it executes.
fn	Function to be called, see below for how it should be declared.
sym	Second argument passed to the function fun when it executes.
argc	Count of arguments in argv. argc is also the third argument passed to the function fun when it executes.
argv	Array containing a variable number of t_atom function arguments. If this argument is non-zero, defer allocates memory to make a copy of the arguments (according to the size passed in argc) and passes the copied array to the function fun when it executes as the fourth argument.

Returns

Return values is for internal Cycling '74 use only.

Remarks

defer_low() always defers a call to the function fun whether you are already in the main thread or not, and uses qelem_set(), not qelem_front(). This function is recommended for responding to messages that will cause your object to open a dialog box, such as read and write.

The deferred function should be declared as follows:

void myobject_do (myObject *client, t_symbol *s, short argc, t_atom *argv);

See also

defer()

long isr

(

void

)

Determine whether your code is executing in the Max scheduler thread.

Returns

This function returns non-zero if you are within Max's scheduler thread, zero otherwise. Note that if your code sets up other types of interrupt-level callbacks, such as for other types of device drivers used in asynchronous mode, isr will return false.

void schedule	(	void *	ob,
		method	fun,
		long	when,
		t_symbol *	sym,
		short	argc,
		t_atom *	argv
	)

Cause a function to be executed at the timer level at some time in the future.

Parameters

ob	First argument passed to the function fun when it executes.
fun	Function to be called, see below for how it should be declared.
when	The logical time that the function fun will be executed.
sym	Second argument passed to the function fun when it executes.
argc	Count of arguments in argv. argc is also the third argument passed to the function fun when it executes.
argv	Array containing a variable number of t_atom function arguments. If this argument is non-zero, defer allocates memory to make a copy of the arguments (according to the size passed in argc) and passes the copied array to the function fun when it executes as the fourth argument.

Remarks

schedule() calls a function at some time in the future. Unlike defer(), the function is called in the scheduling loop when logical time is equal to the specified value when. This means that the function could be called at interrupt level, so it should follow the usual restrictions on interrupt-level conduct. The function fun passed to schedule should be declared as follows:

void myobject_do (myObject *client, t_symbol *s, short argc, t_atom *argv); 

Remarks

One use of schedule() is as an alternative to using the lockout flag.

See also

defer()

void schedule_delay	(	void *	ob,
		method	fun,
		long	delay,
		t_symbol *	sym,
		short	argc,
		t_atom *	argv
	)

Cause a function to be executed at the timer level at some time in the future specified by a delay offset.

Parameters

ob	First argument passed to the function fun when it executes.
fun	Function to be called, see below for how it should be declared.
delay	The delay from the current time before the function will be executed.
sym	Second argument passed to the function fun when it executes.
argc	Count of arguments in argv. argc is also the third argument passed to the function fun when it executes.
argv	Array containing a variable number of t_atom function arguments. If this argument is non-zero, schedule_delay() allocates memory to make a copy of the arguments (according to the size passed in argc) and passes the copied array to the function fun when it executes as the fourth argument.

Remarks

schedule_delay() is similar to schedule() but allows you to specify the time as a delay rather than a specific logical time.

void myobject_click (t_myobject *x, Point pt, short modifiers) 
{ 
   t_atom a[1]; 
   a[0].a_type = A_LONG; 
   a[0].a_w.w_long = Random(); 
   schedule_delay(x, myobject_sched, 0 ,0, 1, a); 
} 

void myobject_sched (t_myobject *x, t_symbol *s, short ac, t_atom *av) 
{ 
   outlet_int(x->m_out,av->a_w.w_long); 
} 

See also

schedule()

long systhread_create	(	method	entryproc,
		void *	arg,
		long	stacksize,
		long	priority,
		long	flags,
		t_systhread *	thread
	)

Create a new thread.

Parameters

entryproc	A method to call in the new thread when the thread is created.
arg	An argument to pass to the method specified for entryproc. Typically this might be a pointer to your object's struct.
stacksize	Not used. Pass 0 for this argument.
priority	Pass 0 for default priority. The priority can range from -32 to 32 where -32 is low, 0 is default and 32 is high.
flags	Not used. Pass 0 for this argument.
thread	The address of a t_systhread where this thread's instance pointer will be stored.

Returns

A Max error code as defined in e_max_errorcodes.

long systhread_detach

(

t_systhread

thread

)

Detach a thread.

After detaching a thread you cannot call systhread_join() on it.

Parameters

thread

The thread to join.

Returns

A Max error code as defined in e_max_errorcodes.

Remarks

You should either call systhread_join() on a thread or systhread_detach() to allow the system to reclaim resources.

void systhread_exit

(

long

status

)

Exit the calling thread.

Call this from within a thread made using systhread_create() when the thread is no longer needed.

Parameters

status

You will typically pass 0 for status. This value will be accessible by systhread_join(), if needed.

int systhread_getpriority

(

t_systhread

thread

)

Get the thread priority for the given thread.

Parameters

thread

The thread for which to find the priority.

Returns

The current priority value for the given thread.

short systhread_isaudiothread

(

void

)

Check to see if the function currently being executed is in an audio thread.

Returns

Returns true if the function is being executed in an audio thread, otherwise false.

short systhread_ismainthread

(

void

)

Check to see if the function currently being executed is in the main thread.

Returns

Returns true if the function is being executed in the main thread, otherwise false.

short systhread_istimerthread

(

void

)

Check to see if the function currently being executed is in a scheduler thread.

Returns

Returns true if the function is being executed in a scheduler thread, otherwise false.

long systhread_join	(	t_systhread	thread,
		unsigned int *	retval
	)

Wait for thread to quit and get return value from systhread_exit().

Parameters

thread	The thread to join.
retval	The address of a long to hold the return value (status) from systhread_exit().

Returns

A Max error code as defined in e_max_errorcodes.

Remarks

If your object is freed, and your thread function accesses memory from your object, then you will obviously have a memory violation. A common use of systhread_join() is to prevent this situation by waiting (in your free method) for the thread to exit.

t_systhread systhread_self

(

void

)

Return the thread instance pointer for the calling thread.

Returns

The thread instance pointer for the thread from which this function is called.

void systhread_setpriority	(	t_systhread	thread,
		int	priority
	)

Set the thread priority for the given thread.

Parameters

thread	The thread for which to set the priority.
priority	A value in the range -32 to 32 where -32 is lowest, 0 is default, and 32 is highest.

void systhread_sleep

(

long

milliseconds

)

Suspend the execution of the calling thread.

Parameters

milliseconds

The number of milliseconds to suspend the execution of the calling thread. The actual amount of time may be longer depending on various factors.

long systhread_terminate

(

t_systhread

thread

)

Forcefully kill a thread – not recommended.

Parameters

thread

The thread to kill.

Returns

A Max error code as defined in e_max_errorcodes.