VipsThreadState

VipsThreadState — pools of worker threads

Stability Level

Stable, unless otherwise indicated

Synopsis

#include <vips/vips.h>

                    VipsThreadState;
                    VipsThreadStateClass;
void *              vips_thread_state_set               (VipsObject *object,
                                                         void *a,
                                                         void *b);
VipsThreadState *   vips_thread_state_new               (VipsImage *im,
                                                         void *a);
VipsThreadState *   (*VipsThreadStartFn)                (VipsImage *im,
                                                         void *a);
int                 (*VipsThreadpoolAllocateFn)         (VipsThreadState *state,
                                                         void *a,
                                                         gboolean *stop);
int                 (*VipsThreadpoolWorkFn)             (VipsThreadState *state,
                                                         void *a);
int                 (*VipsThreadpoolProgressFn)         (void *a);
int                 vips_threadpool_run                 (VipsImage *im,
                                                         VipsThreadStartFn start,
                                                         VipsThreadpoolAllocateFn allocate,
                                                         VipsThreadpoolWorkFn work,
                                                         VipsThreadpoolProgressFn progress,
                                                         void *a);
void                vips_get_tile_size                  (VipsImage *im,
                                                         int *tile_width,
                                                         int *tile_height,
                                                         int *nlines);
void                vips__print_renders                 (void);
void                vips_concurrency_set                (int concurrency);
int                 vips_concurrency_get                (void);

Object Hierarchy

  GObject
   +----VipsObject
         +----VipsThreadState

Description

vips_threadpool_run() loops a set of threads over an image. Threads take it in turns to allocate units of work (a unit might be a tile in an image), then run in parallel to process those units. An optional progress function can be used to give feedback.

Details

VipsThreadState

typedef struct {
	/* Image we run on.
	 */
	VipsImage *im;

	/* This region is created and destroyed by the threadpool for the
	 * use of the worker. 
	 */
	VipsRegion *reg;		

	/* Neither used nor set, do what you like with them.
	 */
	VipsRect pos;
	int x, y;

	/* Set in work to get the allocate to signal stop.
	 */
	gboolean stop;

	/* The client data passed to the enclosing vips_threadpool_run().
	 */
        void *a;
} VipsThreadState;

These per-thread values are carried around for your use by vips_threadpool_run(). They are private to each thread, so they are a useful place for VipsThreadpoolAllocate and VipsThreadpoolWork to communicate.

reg is created for you at the start of processing and freed at the end, but you can do what you like with it.

VipsImage *im;

the VipsImage being operated upon

VipsRegion *reg;

a REGION

VipsRect pos;

a Rect

int x;

an int

int y;

an int

gboolean stop;

void *a;

client data

VipsThreadStateClass

typedef struct {
	VipsObjectClass parent_class;
} VipsThreadStateClass;


vips_thread_state_set ()

void *              vips_thread_state_set               (VipsObject *object,
                                                         void *a,
                                                         void *b);


vips_thread_state_new ()

VipsThreadState *   vips_thread_state_new               (VipsImage *im,
                                                         void *a);


VipsThreadStartFn ()

VipsThreadState *   (*VipsThreadStartFn)                (VipsImage *im,
                                                         void *a);


VipsThreadpoolAllocateFn ()

int                 (*VipsThreadpoolAllocateFn)         (VipsThreadState *state,
                                                         void *a,
                                                         gboolean *stop);

This function is called to allocate a new work unit for the thread. It is always single-threaded, so it can modify per-pool state (such as a counter).

a, b, c are the values supplied to the call to vips_threadpool_run().

It should set stop to TRUE to indicate that no work could be allocated because the job is done.

See also: vips_threadpool_run().

state :

per-thread state

a :

client data

stop :

set this to signal end of computation

Returns :

0 on success, or -1 on error

VipsThreadpoolWorkFn ()

int                 (*VipsThreadpoolWorkFn)             (VipsThreadState *state,
                                                         void *a);

This function is called to process a work unit. Many copies of this can run at once, so it should not write to the per-pool state. It can write to per-thread state.

a, b, c are the values supplied to the call to vips_threadpool_run().

See also: vips_threadpool_run().

state :

per-thread state

a :

client data

Returns :

0 on success, or -1 on error

VipsThreadpoolProgressFn ()

int                 (*VipsThreadpoolProgressFn)         (void *a);

This function is called by the main thread once for every work unit processed. It can be used to give the user progress feedback.

See also: vips_threadpool_run().

a :

client data

Returns :

0 on success, or -1 on error

vips_threadpool_run ()

int                 vips_threadpool_run                 (VipsImage *im,
                                                         VipsThreadStartFn start,
                                                         VipsThreadpoolAllocateFn allocate,
                                                         VipsThreadpoolWorkFn work,
                                                         VipsThreadpoolProgressFn progress,
                                                         void *a);

This function runs a set of threads over an image. Each thread first calls start to create new per-thread state, then runs allocate to set up a new work unit (perhaps the next tile in an image, for example), then work to process that work unit. After each unit is processed, progress is called, so that the operation can give progress feedback. progress may be NULL.

The object returned by start must be an instance of a subclass of VipsThreadState. Use this to communicate between allocate and work.

allocate and start are always single-threaded (so they can write to the per-pool state), whereas work can be executed concurrently. progress is always called by the main thread (ie. the thread which called vips_threadpool_run()).

See also: vips_concurrency_set().

im :

image to loop over

start :

allocate per-thread state

allocate :

allocate a work unit

work :

process a work unit

progress :

give progress feedback about a work unit, or NULL

a :

client data

Returns :

0 on success, or -1 on error.

vips_get_tile_size ()

void                vips_get_tile_size                  (VipsImage *im,
                                                         int *tile_width,
                                                         int *tile_height,
                                                         int *nlines);

Pick a tile size and a buffer height for this image and the current value of vips_concurrency_get(). The buffer height will always be a multiple of tile_height.

im :

image to guess for

tile_width :

return selected tile width

tile_height :

return selected tile height

nlines :

return buffer height in scanlines

vips__print_renders ()

void                vips__print_renders                 (void);


vips_concurrency_set ()

void                vips_concurrency_set                (int concurrency);

Sets the number of worker threads that vips should use when running a VipsThreadPool.

The special value 0 means "default". In this case, the number of threads is set by the environmnt variable IM_CONCURRENCY, or if that is not set, the number of threads availble on the hist machine.

See also: vips_concurrency_get().

concurrency :

number of threads to run

vips_concurrency_get ()

int                 vips_concurrency_get                (void);

Returns the number of worker threads that vips should use when running a VipsThreadPool.

vips gets this values from these sources in turn:

If vips_concurrency_set() has been called, this value is used. The special value 0 means "default". You can also use the command-line argument "--vips-concurrency" to set this value.

If vips_concurrency_set() has not been called and no command-line argument was used, vips uses the value of the environment variable IM_CONCURRENCY,

If IM_CONCURRENCY has not been set, vips find the number of hardware threads that the host machine can run in parallel and uses that value.

The final value is clipped to the range 1 - 1024.

See also: vips_concurrency_get().

Returns :

number of worker threads to use.

See Also

generate