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GNOME Data Access 4 manual | ![]() |
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Top | Description | Object Hierarchy |
#include <libgda/thread-wrapper/gda-thread-wrapper.h> GdaThreadWrapper; GdaThreadWrapper * gda_thread_wrapper_new (void
); gpointer (*GdaThreadWrapperFunc) (gpointer arg
,GError **error
); guint gda_thread_wrapper_execute (GdaThreadWrapper *wrapper
,GdaThreadWrapperFunc func
,gpointer arg
,GDestroyNotify arg_destroy_func
,GError **error
); void (*GdaThreadWrapperVoidFunc) (gpointer arg
,GError **error
); guint gda_thread_wrapper_execute_void (GdaThreadWrapper *wrapper
,GdaThreadWrapperVoidFunc func
,gpointer arg
,GDestroyNotify arg_destroy_func
,GError **error
); gboolean gda_thread_wrapper_cancel (GdaThreadWrapper *wrapper
,guint id
); void gda_thread_wrapper_iterate (GdaThreadWrapper *wrapper
,gboolean may_block
); gpointer gda_thread_wrapper_fetch_result (GdaThreadWrapper *wrapper
,gboolean may_lock
,guint exp_id
,GError **error
); gint gda_thread_wrapper_get_waiting_size (GdaThreadWrapper *wrapper
); void (*GdaThreadWrapperCallback) (GdaThreadWrapper *wrapper
,gpointer instance
,const gchar *signame
,gint n_param_values
,const GValue *param_values
,gpointer gda_reserved
,gpointer data
); gulong gda_thread_wrapper_connect_raw (GdaThreadWrapper *wrapper
,gpointer instance
,const gchar *sig_name
,gboolean private_thread
,gboolean private_job
,GdaThreadWrapperCallback callback
,gpointer data
); void gda_thread_wrapper_disconnect (GdaThreadWrapper *wrapper
,gulong id
); void gda_thread_wrapper_steal_signal (GdaThreadWrapper *wrapper
,gulong id
);
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 exmits 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 user 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 * 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
gpointer (*GdaThreadWrapperFunc) (gpointer arg
,GError **error
);
Specifies the type of function to be passed to gda_thread_wrapper_execute()
.
|
pointer to the data (which is the arg argument passed to gda_thread_wrapper_execute_void() )
|
|
a place to store errors |
Returns : |
a pointer to some data which will be returned by gda_thread_wrapper_fetch_result()
|
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 it is not NULL
, the arg_destroy_func
destruction function is called
on arg
. This occurs in the thread calling gda_thread_wrapper_fetch_result()
.
|
a GdaThreadWrapper object |
|
the function to execute |
|
argument to pass to func
|
|
function to be called when the execution has finished, to destroy arg
|
|
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
void (*GdaThreadWrapperVoidFunc) (gpointer arg
,GError **error
);
Specifies the type of function to be passed to gda_thread_wrapper_execute_void()
.
|
a pointer to the data (which is the arg argument passed to gda_thread_wrapper_execute_void() )
|
|
a place to store errors |
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 it is not NULL
, the arg_destroy_func
destruction function is called
on arg
. This occurs in the thread calling gda_thread_wrapper_fetch_result()
.
|
a GdaThreadWrapper object |
|
the function to execute |
|
argument to pass to func
|
|
function to be called when the execution has finished, to destroy arg
|
|
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
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
|
a GdaThreadWrapper object |
|
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
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. It handles one function's execution result, and
if may_block
is TRUE
, then it will block untill there is one (functions returning void are
ignored).
|
a GdaThreadWrapper object |
|
whether the call may block |
Since 4.2
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()
.
|
a GdaThreadWrapper object |
|
TRUE if this funct must lock the caller untill a result is available |
|
ID of the job for which a result is expected |
|
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
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.
|
a GdaThreadWrapper object |
Returns : |
the number of jobs not yet executed |
Since 4.2
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()
.
|
the GdaThreadWrapper |
|
a pointer to the instance which emitted the signal |
|
the name of the signal being emitted |
|
number of GValue in param_values
|
|
array of n_param_values GValue
|
|
reserved |
|
a pointer to the data (which is the data argument passed to 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
is set to TRUE
, then the callback
function will be called only
if the signal has been emitted by instance
while doing a job on behalf of the current
calling thread. If private
is set to FALSE
, then callback
will be called whenever instance
emits the sig_name
signal.
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()
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.
|
a GdaThreadWrapper object |
|
the instance to connect to |
|
a string of the form "signal-name::detail" |
|
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 th thread in which the
signal is emitted.
|
|
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 .
|
|
a GdaThreadWrapperCallback function. [scope call] |
|
data to pass to callback 's calls. [closure]
|
Returns : |
the handler ID |
Since 4.2
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).
|
a GdaThreadWrapper object |
|
a handler ID, as returned by gda_thread_wrapper_connect_raw()
|
Since 4.2
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.
|
a GdaThreadWrapper object |
|
a signal ID |
Since 4.2