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GLib Reference Manual | |
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#include <glib.h> gint g_atomic_int_get (); void g_atomic_int_set (); void g_atomic_int_add (); gint g_atomic_int_exchange_and_add (); gboolean g_atomic_int_compare_and_exchange (); gpointer g_atomic_pointer_get (); void g_atomic_pointer_set (); gboolean g_atomic_pointer_compare_and_exchange (); void g_atomic_int_inc (gint *atomic); gboolean g_atomic_int_dec_and_test (gint *atomic);
The following functions can be used to atomically access integers and pointers. They are implemented as inline assembler function on most platforms and use slower fall-backs otherwise. Using them can sometimes save you from using a performance-expensive GMutex to protect the integer or pointer.
The most important usage is reference counting. Using
g_atomic_int_inc() and g_atomic_int_dec_and_test() makes reference
counting a very fast operation.
You must not directly read integers or pointers concurrently accessed
by multiple threads, but use the atomic accessor functions instead.
That is, always use g_atomic_int_get() and g_atomic_pointer_get() for
read outs.
They provide the neccessary synchonization mechanisms like memory
barriers to access memory locations concurrently.
If you are using those functions for anything apart from simple
reference counting, you should really be aware of the implications of
doing that. There are literally thousands of ways to shoot yourself in
the foot. So if in doubt, use a GMutex. If you don't know, what
memory barriers are, do not use anything but g_atomic_int_inc() and
g_atomic_int_dec_and_test().
It is not safe to set an integer or pointer just by assigning to it,
when it is concurrently accessed by other threads with the following
functions. Use g_atomic_int_compare_and_exchange() or
g_atomic_pointer_compare_and_exchange() respectively.
gint g_atomic_int_get ();
Reads the value of the integer pointed to by atomic. Also acts as
a memory barrier.
Returns : |
the value of *atomic
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Since 2.4
void g_atomic_int_set ();
Sets the value of the integer pointed to by atomic.
Also acts as a memory barrier.
Since 2.10
void g_atomic_int_add ();
Atomically adds val to the integer pointed to by atomic.
Also acts as a memory barrier.
Since 2.4
gint g_atomic_int_exchange_and_add ();
Atomically adds val to the integer pointed to by atomic. It returns
the value of *atomic just before the addition took place.
Also acts as a memory barrier.
Returns : |
the value of *atomic before the addition.
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Since 2.4
gboolean g_atomic_int_compare_and_exchange ();
Compares oldval with the integer pointed to by atomic and
if they are equal, atomically exchanges *atomic with newval.
Also acts as a memory barrier.
Returns : |
%TRUE, if *atomic was equal oldval. FALSE otherwise.
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Since 2.4
gpointer g_atomic_pointer_get ();
Reads the value of the pointer pointed to by atomic. Also acts as
a memory barrier.
Returns : |
the value to add to *atomic.
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Since 2.4
void g_atomic_pointer_set ();
Sets the value of the pointer pointed to by atomic.
Also acts as a memory barrier.
Since 2.10
gboolean g_atomic_pointer_compare_and_exchange ();
Compares oldval with the pointer pointed to by atomic and
if they are equal, atomically exchanges *atomic with newval.
Also acts as a memory barrier.
Returns : |
%TRUE, if *atomic was equal oldval. FALSE otherwise.
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Since 2.4
void g_atomic_int_inc (gint *atomic);
Atomically increments the integer pointed to by atomic by 1.
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a pointer to an integer. |
Since 2.4