GdaThreadWrapper

GdaThreadWrapper — Execute functions in a sub thread

Stability Level

Stable, unless otherwise indicated

Object Hierarchy

    GObject
    ╰── GdaThreadWrapper

Includes

#include <libgda/thread-wrapper/gda-thread-wrapper.h>

Description

The purpose of the GdaThreadWrapper object is to execute functions in an isolated sub thread. As the GdaThreadWrapper is thread safe, one is able to isolate some code's execution is a private worker thread, and make a non thread safe code thread safe.

The downside of this is that the actual execution of the code will be slower as it requires threads to be synchronized.

The GdaThreadWrapper implements its own locking mechanism and can safely be used from multiple threads at once without needing further locking.

Each thread using a GdaThreadWrapper object can use it as if it was the only user: the GdaThreadWrapper will simply dispatch all the execution requests to its private worker thread and report the execution's status only to the thread which made the request.

The user can also specify a callback function to be called when an object emits a signal while being used by the worker thread, see the gda_thread_wrapper_connect_raw() method.

The following diagram illustrates the conceptual working of the GdaThreadWrapper object: here two user threads are represented (assigned a red and green colors), both using a single GdaThreadWrapper, so in this diagram, 3 threads are present. The communication between the threads are handled by some GAsyncQueue objects (in a transparent way for the user, presented here only for illustration purposes). The queue represented in yellow is where jobs are pushed by each user thread (step 1), and popped by the worker thread (step 2). Once the worker thread has finished with a job, it stores the result along with the job and pushes it to the queue dedicated to the user thread (step 3) in this example the red queue (because the job was issued from the thread represented in red). The last step is when the user fetches the result (in its user thread), step 4.

If, when the worker thread is busy with a job, a signal is emitted, and if the user has set up a signal handler using gda_thread_wrapper_connect_raw(), then a "job as signal" is created by the worker thread and pushed to the user thread as illustrated at the bottom of the diagram.

GdaThreadWrapper's conceptual working

It's the user's responsability to regularly check if a submitted job has completed (using gda_thread_wrapper_fetch_result()) or if a signal has been emitted by an object while in the worker thread and needs to be handled by the GdaThreadWrapper to call the associated callback (using gda_thread_wrapper_iterate() or automatically done when calling gda_thread_wrapper_fetch_result()).

However, when a main loop is available, the GdaThreadWrapper can emit notifications through a GIOChannel which can be intregated in the main loop. The GIOChannel can be created using gda_thread_wrapper_get_io_channel().

Functions

gda_thread_wrapper_new ()

GdaThreadWrapper *
gda_thread_wrapper_new (void);

Creates a new GdaThreadWrapper object

Returns

a new GdaThreadWrapper object, or NULL if threads are not supported/enabled

Since 4.2


gda_thread_wrapper_get_io_channel ()

GIOChannel *
gda_thread_wrapper_get_io_channel (GdaThreadWrapper *wrapper);

Allow wrapper to notify when an execution job is finished, by making its exec ID readable through a new GIOChannel. This function is useful when the notification needs to be included into a main loop. This also notifies that signals (emitted by objects in wrapper 's internal thread) are available.

The returned GIOChannel will have something to read everytime an execution job is finished for an execution job submitted from the calling thread. The user whould read GdaThreadNotification structures from the channel and analyse its contents to call gda_thread_wrapper_iterate() or gda_thread_wrapper_fetch_result().

Note1: the new communication channel will only be operational for jobs submitted after this function returns, and for signals which have been connected after this function returns. A safe practice is to call this function before the wrapper object has been used.

Note2: this function will return the same GIOChannel everytime it's called from the same thread.

Note3: if the usage of the returned GIOChannel reveals an error, then g_io_channel_shutdown() and g_io_channel_unref() should be called on the GIOChannel to let wrapper know it should not use that object anymore.

Parameters

wrapper

a GdaThreadWrapper object

 

Returns

a new GIOChannel, or NULL if it could not be created.

[transfer none]

Since 4.2.9


gda_thread_wrapper_unset_io_channel ()

void
gda_thread_wrapper_unset_io_channel (GdaThreadWrapper *wrapper);

Does the opposite of gda_thread_wrapper_get_io_channel()

Parameters

wrapper

a GdaThreadWrapper

 

Since 4.2.9


GdaThreadWrapperFunc ()

gpointer
(*GdaThreadWrapperFunc) (gpointer arg,
                         GError **error);

Specifies the type of function to be passed to gda_thread_wrapper_execute().

Parameters

arg

pointer to the data (which is the arg argument passed to gda_thread_wrapper_execute_void())

 

error

a place to store errors

 

Returns

a pointer to some data which will be returned by gda_thread_wrapper_fetch_result()


gda_thread_wrapper_execute ()

guint
gda_thread_wrapper_execute (GdaThreadWrapper *wrapper,
                            GdaThreadWrapperFunc func,
                            gpointer arg,
                            GDestroyNotify arg_destroy_func,
                            GError **error);

Make wrapper execute the func function with the arg argument (along with a GError which is not error ) in the sub thread managed by wrapper . To execute a function which does not return anything, use gda_thread_wrapper_execute_void().

This method returns immediately, and the caller then needs to use gda_thread_wrapper_fetch_result() to check if the execution has finished and get the result.

Once func 's execution is finished, if arg is not NULL, the arg_destroy_func destruction function is called on arg . This call occurs in the thread calling gda_thread_wrapper_fetch_result().

If an error occurred in this function, then the arg_destroy_func function is not called to free arg .

Parameters

wrapper

a GdaThreadWrapper object

 

func

the function to execute, not NULL

 

arg

argument to pass to func , or NULL.

[allow-none]

arg_destroy_func

function to be called when the execution has finished, to destroy arg , or NULL.

[allow-none]

error

a place to store errors, for errors occurring in this method, not errors occurring while func is executed, or NULL

 

Returns

the job ID, or 0 if an error occurred

Since 4.2


GdaThreadWrapperVoidFunc ()

void
(*GdaThreadWrapperVoidFunc) (gpointer arg,
                             GError **error);

Specifies the type of function to be passed to gda_thread_wrapper_execute_void().

Parameters

arg

a pointer to the data (which is the arg argument passed to gda_thread_wrapper_execute_void())

 

error

a place to store errors

 

gda_thread_wrapper_execute_void ()

guint
gda_thread_wrapper_execute_void (GdaThreadWrapper *wrapper,
                                 GdaThreadWrapperVoidFunc func,
                                 gpointer arg,
                                 GDestroyNotify arg_destroy_func,
                                 GError **error);

Make wrapper execute the func function with the arg argument (along with a GError which is not error ) in the sub thread managed by wrapper . To execute a function which returns some pointer, use gda_thread_wrapper_execute().

This method returns immediately. Calling gda_thread_wrapper_fetch_result() is not necessary as func does not return any result. However, it may be necessary to call gda_thread_wrapper_iterate() to give wrapper a chance to execute the arg_destroy_func function if not NULL (note that gda_thread_wrapper_iterate() is called by gda_thread_wrapper_fetch_result() itself).

Once func 's execution is finished, if arg is not NULL, the arg_destroy_func destruction function is called on arg . This call occurs in the thread calling gda_thread_wrapper_fetch_result().

If an error occurred in this function, then the arg_destroy_func function is not called to free arg .

Parameters

wrapper

a GdaThreadWrapper object

 

func

the function to execute, not NULL

 

arg

argument to pass to func .

[allow-none]

arg_destroy_func

function to be called when the execution has finished, to destroy arg , or NULL.

[allow-none]

error

a place to store errors, for errors occurring in this method, not errors occurring while func is executed, or NULL

 

Returns

the job ID, or 0 if an error occurred

Since 4.2


gda_thread_wrapper_cancel ()

gboolean
gda_thread_wrapper_cancel (GdaThreadWrapper *wrapper,
                           guint id);

Cancels a job not yet executed. This may fail for the following reasons:

  • the job id could not be found, either because it has already been treated or because it does not exist or because it was created in another thread

  • the job id is currently being treated by the worker thread

Parameters

wrapper

a GdaThreadWrapper object

 

id

the ID of a job as returned by gda_thread_wrapper_execute() or gda_thread_wrapper_execute_void()

 

Returns

TRUE if the job has been cancelled, or FALSE in any other case.

Since 4.2


gda_thread_wrapper_iterate ()

void
gda_thread_wrapper_iterate (GdaThreadWrapper *wrapper,
                            gboolean may_block);

This method gives wrapper a chance to check if some functions to be executed have finished for the calling thread. In this case it handles the execution result and makes it ready to be processed using gda_thread_wrapper_fetch_result().

This method also allows wrapper to handle signals which may have been emitted by objects while in the worker thread, and call the callback function specified when gda_thread_wrapper_connect_raw() was used.

If may_block is TRUE, then it will block untill there is one finished execution (functions returning void and signals are ignored regarding this argument).

Parameters

wrapper

a GdaThreadWrapper object

 

may_block

whether the call may block

 

Since 4.2


gda_thread_wrapper_fetch_result ()

gpointer
gda_thread_wrapper_fetch_result (GdaThreadWrapper *wrapper,
                                 gboolean may_lock,
                                 guint exp_id,
                                 GError **error);

Use this method to check if the execution of a function is finished. The function's execution must have been requested using gda_thread_wrapper_execute().

Parameters

wrapper

a GdaThreadWrapper object

 

may_lock

TRUE if this funct must lock the caller untill a result is available

 

exp_id

ID of the job for which a result is expected

 

error

a place to store errors, for errors which may have occurred during the execution, or NULL

 

Returns

the pointer returned by the execution, or NULL if no result is available.

[transfer none][allow-none]

Since 4.2


gda_thread_wrapper_get_waiting_size ()

gint
gda_thread_wrapper_get_waiting_size (GdaThreadWrapper *wrapper);

Use this method to query the number of functions which have been queued to be executed but which have not yet been executed.

Parameters

wrapper

a GdaThreadWrapper object

 

Returns

the number of jobs not yet executed

Since 4.2


GdaThreadWrapperCallback ()

void
(*GdaThreadWrapperCallback) (GdaThreadWrapper *wrapper,
                             gpointer instance,
                             const gchar *signame,
                             gint n_param_values,
                             const GValue *param_values,
                             gpointer gda_reserved,
                             gpointer data);

Specifies the type of function to be passed to gda_thread_wrapper_connect_raw()

Parameters

wrapper

the GdaThreadWrapper

 

instance

a pointer to the instance which emitted the signal

 

signame

the name of the signal being emitted

 

n_param_values

number of GValue in param_values

 

param_values

array of n_param_values GValue

 

gda_reserved

reserved

 

data

a pointer to the data (which is the data argument passed to gda_thread_wrapper_connect_raw())

 

gda_thread_wrapper_connect_raw ()

gulong
gda_thread_wrapper_connect_raw (GdaThreadWrapper *wrapper,
                                gpointer instance,
                                const gchar *sig_name,
                                gboolean private_thread,
                                gboolean private_job,
                                GdaThreadWrapperCallback callback,
                                gpointer data);

Connects a callback function to a signal for a particular object. The difference with g_signal_connect() and similar functions are:

  • the callback argument is not a GCallback function, so the callback signature is not dependent on the signal itself

  • the signal handler must not have to return any value

  • the callback function will be called asynchronously, the caller may need to use gda_thread_wrapper_iterate() to get the notification

  • if private_job and private_thread control in which case the signal is propagated.

Also note that signal handling is done asynchronously: when emitted in the worker thread, it will be "queued" to be processed in the user thread when it has the chance (when gda_thread_wrapper_iterate() is called directly or indirectly). The side effect is that the callback function is usually called long after the object emitting the signal has finished emitting it.

To disconnect a signal handler, don't use any of the g_signal_handler_*() functions but the gda_thread_wrapper_disconnect() method.

Parameters

wrapper

a GdaThreadWrapper object

 

instance

the instance to connect to

 

sig_name

a string of the form "signal-name::detail"

 

private_thread

set to TRUE if callback is to be invoked only if the signal has been emitted while in wrapper 's private sub thread (ie. used when wrapper is executing some functions specified by gda_thread_wrapper_execute() or gda_thread_wrapper_execute_void()), and to FALSE if the callback is to be invoked whenever the signal is emitted, independently of the thread in which the signal is emitted.

 

private_job

set to TRUE if callback is to be invoked only if the signal has been emitted when a job created for the calling thread is being executed, and to FALSE if callback has to be called whenever the sig_name signal is emitted by instance . Note that this argument is not taken into account if private_thread is set to FALSE.

 

callback

a GdaThreadWrapperCallback function.

[scope call]

data

data to pass to callback 's calls.

[closure]

Returns

the handler ID

Since 4.2


gda_thread_wrapper_disconnect ()

void
gda_thread_wrapper_disconnect (GdaThreadWrapper *wrapper,
                               gulong id);

Disconnects the emission of a signal, does the opposite of gda_thread_wrapper_connect_raw().

As soon as this method returns, the callback function set when gda_thread_wrapper_connect_raw() was called will not be called anymore (even if the object has emitted the signal in the worker thread and this signal has not been handled in the user thread).

Parameters

wrapper

a GdaThreadWrapper object

 

id

a handler ID, as returned by gda_thread_wrapper_connect_raw()

 

Since 4.2


gda_thread_wrapper_steal_signal ()

void
gda_thread_wrapper_steal_signal (GdaThreadWrapper *wrapper,
                                 gulong id);

Requests that the signal which ID is id (which has been obtained using gda_thread_wrapper_connect_raw()) be treated by the calling thread instead of by the thread in which gda_thread_wrapper_connect_raw() was called.

Parameters

wrapper

a GdaThreadWrapper object

 

id

a signal ID

 

Since 4.2

Types and Values

struct GdaThreadWrapper

struct GdaThreadWrapper;

GdaThreadNotification

typedef struct {
	GdaThreadNotificationType type;
	guint                     job_id;
} GdaThreadNotification;

A notification to be read through the GIOChannel which is returned by gda_thread_wrapper_get_io_channel(), for example:

gboolean
wrapper_ioc_cb (GIOChannel *source, GIOCondition condition, gpointer data)
{
    GIOStatus status;
    gsize nread;
    GdaThreadNotification notif;
    if (condition & G_IO_IN) {
   status = g_io_channel_read_chars (source, (gchar*) &notif, sizeof (notif), &nread, NULL);
        if ((status != G_IO_STATUS_NORMAL) || (nread != sizeof (notif)))
            goto onerror;
   switch (notif.type) {
   case GDA_THREAD_NOTIFICATION_JOB:
            check_for_wrapper_result (bcnc);
            break;
        case GDA_THREAD_NOTIFICATION_SIGNAL:
            gda_thread_wrapper_iterate (bcnc->priv->wrapper, FALSE);
            break;
        default:
            goto onerror;
            break;
   }
  }
  if (condition & (G_IO_ERR | G_IO_HUP | G_IO_NVAL))
            goto onerror;
  return TRUE; // keep callback

onerror:
  g_io_channel_shutdown (bcnc->priv->ioc, FALSE, NULL);
  return FALSE; // removed callback
}

{
[...]
    GIOChannel *ioc;
    ioc = gda_thread_wrapper_get_io_channel (wrapper);
    if (!ioc)
        [handle error]
    else {
        guint watch_id;
        watch_id = g_io_add_watch (ioc, G_IO_IN | G_IO_HUP | G_IO_ERR | G_IO_NVAL,
                                   (GIOFunc) wrapper_ioc_cb, NULL);
    }
}

Members

GdaThreadNotificationType type;

the notification type

 

guint job_id;

the job ID, if type is a GDA_THREAD_NOTIFICATION_JOB

 

enum GdaThreadNotificationType

Defines the kind of notification which can be obtained when reading from te GIOChannel returned by gda_thread_wrapper_get_io_channel().

Members

GDA_THREAD_NOTIFICATION_JOB

the notification regards a job finished

 

GDA_THREAD_NOTIFICATION_SIGNAL

the notification regards a signal