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c4c76d77cb
The existing g_pointer_bit_lock() and g_pointer_bit_unlock() API
requires the user to understand/reimplement how bits of the pointer get
mangled. Add helper functions for that.
The useful thing to do with g_pointer_bit_lock() API is to get/set
pointers while having it locked. For example, to set the pointer a user
can do:
g_pointer_bit_lock (&lockptr, lock_bit);
ptr2 = set_bit_pointer_as_if_locked(ptr, lock_bit);
g_atomic_pointer_set (&lockptr, ptr2);
g_pointer_bit_unlock (&lockptr, lock_bit);
That has several problems:
- it requires one extra atomic operations (3 instead of 2, in the
non-contended case).
- the first g_atomic_pointer_set() already wakes blocked threads,
which find themselves still being locked and needs to go back to
sleep.
- the user needs to re-implement how bit-locking mangles the pointer so
that it looks as if it were locked.
- while the user tries to re-implement what glib does to mangle the
pointer for bitlocking, there is no immediate guarantee that they get
it right.
Now we can do instead:
g_pointer_bit_lock(&lockptr, lock_bit);
g_pointer_bit_unlock_and_set(&lockptr, lock_bit, ptr, 0);
This will also emit a critical if @ptr has the locked bit set.
g_pointer_bit_lock() really only works with pointers that have a certain
alignment, and the lowest bits unset. Otherwise, there is no space to
encode both the locking and all pointer values. The new assertion helps
to catch such bugs.
Also, g_pointer_bit_lock_mask_ptr() is here, so we can do:
g_pointer_bit_lock(&lockptr, lock_bit);
/* set a pointer separately, when g_pointer_bit_unlock_and_set() is unsuitable. */
g_atomic_pointer_set(&lockptr, g_pointer_bit_lock_mask_ptr(ptr, lock_bit, TRUE, 0, NULL));
...
g_pointer_bit_unlock(&lockptr, lock_bit);
and:
g_pointer_bit_lock(&lockptr, lock_bit);
/* read the real pointer after getting the lock. */
ptr = g_pointer_bit_lock_mask_ptr(lockptr, lock_bit, FALSE, 0, NULL));
...
g_pointer_bit_unlock(&lockptr, lock_bit);
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| .. | ||
| performance | ||
| accumulator.c | ||
| autoptr.c | ||
| basic-signals.c | ||
| basics-gobject.c | ||
| binding.c | ||
| bindinggroup.c | ||
| boxed.c | ||
| closure-refcount.c | ||
| closure.c | ||
| custom-dispatch.c | ||
| cxx.cpp | ||
| defaultiface.c | ||
| deftype.c | ||
| deprecated-properties.c | ||
| dynamictests.c | ||
| dynamictype.c | ||
| enums.c | ||
| flags.c | ||
| genmarshal.py | ||
| gobject-query.py | ||
| ifaceproperties.c | ||
| marshalers.list | ||
| max-version.c | ||
| meson.build | ||
| mkenums.py | ||
| notify-init2.c | ||
| notify-init.c | ||
| object.c | ||
| objects-refcount1.c | ||
| objects-refcount2.c | ||
| override.c | ||
| param.c | ||
| private.c | ||
| properties-introspection.c | ||
| properties-refcount1.c | ||
| properties-refcount2.c | ||
| properties-refcount3.c | ||
| properties-refcount4.c | ||
| properties.c | ||
| qdata.c | ||
| reference.c | ||
| references.c | ||
| signal-handler.c | ||
| signalgroup.c | ||
| signals-refcount.c | ||
| signals.c | ||
| singleton.c | ||
| taptestrunner.py | ||
| testcommon.h | ||
| testing.c | ||
| testmodule.c | ||
| testmodule.h | ||
| threadtests.c | ||
| type-flags.c | ||
| type.c | ||
| value.c | ||