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GstPoll

GstPoll — Keep track of file descriptors and make it possible to wait on them in a cancellable way

Types and Values

Includes

#include <gst/gst.h>

Description

A GstPoll keeps track of file descriptors much like fd_set (used with select()) or a struct pollfd array (used with poll()). Once created with gst_poll_new(), the set can be used to wait for file descriptors to be readable and/or writable. It is possible to make this wait be controlled by specifying TRUE for the controllable flag when creating the set (or later calling gst_poll_set_controllable()).

New file descriptors are added to the set using gst_poll_add_fd(), and removed using gst_poll_remove_fd(). Controlling which file descriptors should be waited for to become readable and/or writable are done using gst_poll_fd_ctl_read() and gst_poll_fd_ctl_write().

Use gst_poll_wait() to wait for the file descriptors to actually become readable and/or writable, or to timeout if no file descriptor is available in time. The wait can be controlled by calling gst_poll_restart() and gst_poll_set_flushing().

Once the file descriptor set has been waited for, one can use gst_poll_fd_has_closed() to see if the file descriptor has been closed, gst_poll_fd_has_error() to see if it has generated an error, gst_poll_fd_can_read() to see if it is possible to read from the file descriptor, and gst_poll_fd_can_write() to see if it is possible to write to it.

Functions

gst_poll_add_fd ()

gboolean
gst_poll_add_fd (GstPoll *set,
                 GstPollFD *fd);

Add a file descriptor to the file descriptor set.

Parameters

set

a file descriptor set.

 

fd

a file descriptor.

 

Returns

TRUE if the file descriptor was successfully added to the set.


gst_poll_fd_can_read ()

gboolean
gst_poll_fd_can_read (const GstPoll *set,
                      GstPollFD *fd);

Check if fd in set has data to be read.

Parameters

set

a file descriptor set.

 

fd

a file descriptor.

 

Returns

TRUE if the descriptor has data to be read.


gst_poll_fd_can_write ()

gboolean
gst_poll_fd_can_write (const GstPoll *set,
                       GstPollFD *fd);

Check if fd in set can be used for writing.

Parameters

set

a file descriptor set.

 

fd

a file descriptor.

 

Returns

TRUE if the descriptor can be used for writing.


gst_poll_fd_ctl_read ()

gboolean
gst_poll_fd_ctl_read (GstPoll *set,
                      GstPollFD *fd,
                      gboolean active);

Control whether the descriptor fd in set will be monitored for readability.

Parameters

set

a file descriptor set.

 

fd

a file descriptor.

 

active

a new status.

 

Returns

TRUE if the descriptor was successfully updated.


gst_poll_fd_ctl_write ()

gboolean
gst_poll_fd_ctl_write (GstPoll *set,
                       GstPollFD *fd,
                       gboolean active);

Control whether the descriptor fd in set will be monitored for writability.

Parameters

set

a file descriptor set.

 

fd

a file descriptor.

 

active

a new status.

 

Returns

TRUE if the descriptor was successfully updated.


gst_poll_fd_has_closed ()

gboolean
gst_poll_fd_has_closed (const GstPoll *set,
                        GstPollFD *fd);

Check if fd in set has closed the connection.

Parameters

set

a file descriptor set.

 

fd

a file descriptor.

 

Returns

TRUE if the connection was closed.


gst_poll_fd_has_error ()

gboolean
gst_poll_fd_has_error (const GstPoll *set,
                       GstPollFD *fd);

Check if fd in set has an error.

Parameters

set

a file descriptor set.

 

fd

a file descriptor.

 

Returns

TRUE if the descriptor has an error.


gst_poll_fd_ignored ()

void
gst_poll_fd_ignored (GstPoll *set,
                     GstPollFD *fd);

Mark fd as ignored so that the next call to gst_poll_wait() will yield the same result for fd as last time. This function must be called if no operation (read/write/recv/send/etc.) will be performed on fd before the next call to gst_poll_wait().

The reason why this is needed is because the underlying implementation might not allow querying the fd more than once between calls to one of the re-enabling operations.

Parameters

set

a file descriptor set.

 

fd

a file descriptor.

 

gst_poll_fd_init ()

void
gst_poll_fd_init (GstPollFD *fd);

Initializes fd . Alternatively you can initialize it with GST_POLL_FD_INIT.

Parameters

fd

a GstPollFD

 

gst_poll_free ()

void
gst_poll_free (GstPoll *set);

Free a file descriptor set.

Parameters

set

a file descriptor set.

[transfer full]

gst_poll_new ()

GstPoll *
gst_poll_new (gboolean controllable);

Create a new file descriptor set. If controllable , it is possible to restart or flush a call to gst_poll_wait() with gst_poll_restart() and gst_poll_set_flushing() respectively.

Free-function: gst_poll_free

[skip]

Parameters

controllable

whether it should be possible to control a wait.

 

Returns

a new GstPoll, or NULL in case of an error. Free with gst_poll_free().

[transfer full][nullable]


gst_poll_new_timer ()

GstPoll *
gst_poll_new_timer (void);

Create a new poll object that can be used for scheduling cancellable timeouts.

A timeout is performed with gst_poll_wait(). Multiple timeouts can be performed from different threads.

Free-function: gst_poll_free

[skip]

Returns

a new GstPoll, or NULL in case of an error. Free with gst_poll_free().

[transfer full][nullable]


gst_poll_get_read_gpollfd ()

void
gst_poll_get_read_gpollfd (GstPoll *set,
                           GPollFD *fd);

Get a GPollFD for the reading part of the control socket. This is useful when integrating with a GSource and GMainLoop.

Parameters

set

a GstPoll

 

fd

a GPollFD

 

gst_poll_remove_fd ()

gboolean
gst_poll_remove_fd (GstPoll *set,
                    GstPollFD *fd);

Remove a file descriptor from the file descriptor set.

Parameters

set

a file descriptor set.

 

fd

a file descriptor.

 

Returns

TRUE if the file descriptor was successfully removed from the set.


gst_poll_restart ()

void
gst_poll_restart (GstPoll *set);

Restart any gst_poll_wait() that is in progress. This function is typically used after adding or removing descriptors to set .

If set is not controllable, then this call will have no effect.

This function only works for non-timer GstPoll objects created with gst_poll_new().

Parameters

set

a GstPoll.

 

gst_poll_set_controllable ()

gboolean
gst_poll_set_controllable (GstPoll *set,
                           gboolean controllable);

When controllable is TRUE, this function ensures that future calls to gst_poll_wait() will be affected by gst_poll_restart() and gst_poll_set_flushing().

This function only works for non-timer GstPoll objects created with gst_poll_new().

Parameters

set

a GstPoll.

 

controllable

new controllable state.

 

Returns

TRUE if the controllability of set could be updated.


gst_poll_set_flushing ()

void
gst_poll_set_flushing (GstPoll *set,
                       gboolean flushing);

When flushing is TRUE, this function ensures that current and future calls to gst_poll_wait() will return -1, with errno set to EBUSY.

Unsetting the flushing state will restore normal operation of set .

This function only works for non-timer GstPoll objects created with gst_poll_new().

Parameters

set

a GstPoll.

 

flushing

new flushing state.

 

gst_poll_wait ()

gint
gst_poll_wait (GstPoll *set,
               GstClockTime timeout);

Wait for activity on the file descriptors in set . This function waits up to the specified timeout . A timeout of GST_CLOCK_TIME_NONE waits forever.

For GstPoll objects created with gst_poll_new(), this function can only be called from a single thread at a time. If called from multiple threads, -1 will be returned with errno set to EPERM.

This is not true for timer GstPoll objects created with gst_poll_new_timer(), where it is allowed to have multiple threads waiting simultaneously.

Parameters

set

a GstPoll.

 

timeout

a timeout in nanoseconds.

 

Returns

The number of GstPollFD in set that have activity or 0 when no activity was detected after timeout . If an error occurs, -1 is returned and errno is set.


gst_poll_read_control ()

gboolean
gst_poll_read_control (GstPoll *set);

Read a byte from the control socket of the controllable set .

This function only works for timer GstPoll objects created with gst_poll_new_timer().

Parameters

set

a GstPoll.

 

Returns

TRUE on success. FALSE when when there was no byte to read or reading the byte failed. If there was no byte to read, and only then, errno will contain EWOULDBLOCK or EAGAIN. For all other values of errno this always signals a critical error.


gst_poll_write_control ()

gboolean
gst_poll_write_control (GstPoll *set);

Write a byte to the control socket of the controllable set . This function is mostly useful for timer GstPoll objects created with gst_poll_new_timer().

It will make any current and future gst_poll_wait() function return with 1, meaning the control socket is set. After an equal amount of calls to gst_poll_read_control() have been performed, calls to gst_poll_wait() will block again until their timeout expired.

This function only works for timer GstPoll objects created with gst_poll_new_timer().

Parameters

set

a GstPoll.

 

Returns

TRUE on success. FALSE when when the byte could not be written. errno contains the detailed error code but will never be EAGAIN, EINTR or EWOULDBLOCK. FALSE always signals a critical error.

Types and Values

GstPoll

typedef struct _GstPoll GstPoll;

A set of file/network descriptors.


GstPollFD

typedef struct {
  int fd;
} GstPollFD;

A file descriptor object.

Members

int fd;

a file descriptor

 

GST_POLL_FD_INIT

#define GST_POLL_FD_INIT  { -1, -1 }

A GstPollFD must be initialized with this macro, before it can be used. This macro can used be to initialize a variable, but it cannot be assigned to a variable. In that case you have to use gst_poll_fd_init().

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