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Implement pointer sized bitlocks
Based on a patch from Alexander Larsson. https://bugzilla.gnome.org/show_bug.cgi?id=651467
This commit is contained in:
parent
1a80405a36
commit
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193
glib/gbitlock.c
193
glib/gbitlock.c
@ -22,6 +22,7 @@
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#include "gbitlock.h"
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#include <glib/gmessages.h>
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#include <glib/gatomic.h>
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#include <glib/gslist.h>
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#include <glib/gthread.h>
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@ -334,3 +335,195 @@ g_bit_unlock (volatile gint *address,
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g_futex_wake (address);
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}
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}
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/* We emulate pointer-sized futex(2) because the kernel API only
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* supports integers.
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*
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* We assume that the 'interesting' part is always the lower order bits.
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* This assumption holds because pointer bitlocks are restricted to
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* using the low order bits of the pointer as the lock.
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*
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* On 32 bits, there is nothing to do since the pointer size is equal to
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* the integer size. On little endian the lower-order bits don't move,
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* so do nothing. Only on 64bit big endian do we need to do a bit of
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* pointer arithmetic: the low order bits are shifted by 4 bytes. We
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* have a helper function that always does the right thing here.
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*
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* Since we always consider the low-order bits of the integer value, a
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* simple cast from (gsize) to (guint) always takes care of that.
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*
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* After that, pointer-sized futex becomes as simple as:
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*
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* g_futex_wait (g_futex_int_address (address), (guint) value);
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*
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* and
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*
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* g_futex_wake (g_futex_int_address (int_address));
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*/
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static const volatile gint *
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g_futex_int_address (const volatile void *address)
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{
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const volatile gint *int_address = address;
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#if G_BYTE_ORDER == G_BIG_ENDIAN && GLIB_SIZEOF_VOID_P == 8
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int_address++;
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#endif
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return int_address;
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}
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/**
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* g_pointer_bit_lock:
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* @address: a pointer to a #gpointer-sized value
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* @lock_bit: a bit value between 0 and 31
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*
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* This is equivalent to g_bit_lock, but working on pointers (or other
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* pointer-sized values).
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*
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* For portability reasons, you may only lock on the bottom 32 bits of
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* the pointer.
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*
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* Since: 2.30
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**/
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void
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(g_pointer_bit_lock) (volatile void *address,
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gint lock_bit)
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{
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g_return_if_fail (lock_bit < 32);
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{
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#if defined (__GNUC__) && (defined (i386) || defined (__amd64__))
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retry:
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asm volatile goto ("lock bts %1, (%0)\n"
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"jc %l[contended]"
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: /* no output */
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: "r" (address), "r" ((gsize) lock_bit)
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: "cc", "memory"
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: contended);
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return;
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contended:
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{
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volatile gsize *pointer_address = address;
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gsize mask = 1u << lock_bit;
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gsize v;
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v = (gsize) g_atomic_pointer_get (pointer_address);
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if (v & mask)
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{
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guint class = ((gsize) address) % G_N_ELEMENTS (g_bit_lock_contended);
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g_atomic_int_add (&g_bit_lock_contended[class], +1);
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g_futex_wait (g_futex_int_address (address), v);
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g_atomic_int_add (&g_bit_lock_contended[class], -1);
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}
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}
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goto retry;
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#else
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volatile gsize *pointer_address = address;
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gsize mask = 1u << lock_bit;
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gsize v;
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retry:
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v = g_atomic_pointer_or (pointer_address, mask);
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if (v & mask)
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/* already locked */
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{
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guint class = ((gsize) address) % G_N_ELEMENTS (g_bit_lock_contended);
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g_atomic_int_add (&g_bit_lock_contended[class], +1);
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g_futex_wait (g_futex_int_address (address), (guint) v);
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g_atomic_int_add (&g_bit_lock_contended[class], -1);
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goto retry;
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}
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#endif
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}
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}
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/**
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* g_pointer_bit_trylock:
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* @address: a pointer to a #gpointer-sized value
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* @lock_bit: a bit value between 0 and 31
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* @returns: %TRUE if the lock was acquired
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*
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* This is equivalent to g_bit_trylock, but working on pointers (or
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* other pointer-sized values).
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*
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* For portability reasons, you may only lock on the bottom 32 bits of
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* the pointer.
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*
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* Since: 2.30
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**/
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gboolean
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(g_pointer_bit_trylock) (volatile void *address,
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gint lock_bit)
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{
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g_return_val_if_fail (lock_bit < 32, FALSE);
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{
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#if defined (__GNUC__) && (defined (i386) || defined (__amd64__))
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gboolean result;
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asm volatile ("lock bts %2, (%1)\n"
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"setnc %%al\n"
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"movzx %%al, %0"
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: "=r" (result)
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: "r" (address), "r" ((gsize) lock_bit)
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: "cc", "memory");
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return result;
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#else
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volatile gsize *pointer_address = address;
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gsize mask = 1u << lock_bit;
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gsize v;
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g_return_val_if_fail (lock_bit < 32, FALSE);
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v = g_atomic_pointer_or (pointer_address, mask);
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return ~v & mask;
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#endif
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}
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}
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/**
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* g_pointer_bit_unlock:
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* @address: a pointer to a #gpointer-sized value
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* @lock_bit: a bit value between 0 and 31
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*
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* This is equivalent to g_bit_unlock, but working on pointers (or other
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* pointer-sized values).
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*
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* For portability reasons, you may only lock on the bottom 32 bits of
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* the pointer.
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*
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* Since: 2.30
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**/
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void
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(g_pointer_bit_unlock) (volatile void *address,
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gint lock_bit)
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{
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g_return_if_fail (lock_bit < 32);
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{
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#if defined (__GNUC__) && (defined (i386) || defined (__amd64__))
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asm volatile ("lock btr %1, (%0)"
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: /* no output */
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: "r" (address), "r" ((gsize) lock_bit)
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: "cc", "memory");
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#else
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volatile gsize *pointer_address = address;
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gsize mask = 1u << lock_bit;
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g_atomic_pointer_and (pointer_address, ~mask);
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#endif
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{
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guint class = ((gsize) address) % G_N_ELEMENTS (g_bit_lock_contended);
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if (g_atomic_int_get (&g_bit_lock_contended[class]))
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g_futex_wake (g_futex_int_address (address));
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}
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}
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}
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@ -38,6 +38,35 @@ gboolean g_bit_trylock (volatile gint *address,
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void g_bit_unlock (volatile gint *address,
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gint lock_bit);
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void g_pointer_bit_lock (volatile void *address,
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gint lock_bit);
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gboolean g_pointer_bit_trylock (volatile void *address,
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gint lock_bit);
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void g_pointer_bit_unlock (volatile void *address,
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gint lock_bit);
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#ifdef __GNUC__
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#define g_pointer_bit_lock(address, lock_bit) \
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(G_GNUC_EXTENSION ({ \
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G_STATIC_ASSERT (sizeof *(address) == sizeof (gpointer)); \
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g_pointer_bit_lock ((address), (lock_bit)); \
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}))
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#define g_pointer_bit_trylock(address, lock_bit) \
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(G_GNUC_EXTENSION ({ \
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G_STATIC_ASSERT (sizeof *(address) == sizeof (gpointer)); \
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g_pointer_bit_trylock ((address), (lock_bit)); \
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}))
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#define g_pointer_bit_unlock(address, lock_bit) \
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(G_GNUC_EXTENSION ({ \
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G_STATIC_ASSERT (sizeof *(address) == sizeof (gpointer)); \
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g_pointer_bit_unlock ((address), (lock_bit)); \
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}))
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#endif
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G_END_DECLS
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#endif /* __G_BITLOCK_H_ */
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@ -1065,6 +1065,9 @@ g_string_append_c
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g_bit_lock
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g_bit_trylock
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g_bit_unlock
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g_pointer_bit_lock
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g_pointer_bit_trylock
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g_pointer_bit_unlock
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g_once_impl
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g_once_init_enter_impl
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g_once_init_leave
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#define ITERATIONS 10000
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#define THREADS 100
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#include <glib.h>
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#if TEST_EMULATED_FUTEX
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/* this is defined for the 1bit-mutex-emufutex test.
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@ -31,9 +32,16 @@
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/* rebuild gbitlock.c without futex support,
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defining our own version of the g_bit_*lock symbols
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*/
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#undef g_pointer_bit_lock
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#undef g_pointer_bit_trylock
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#undef g_pointer_bit_unlock
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#define g_bit_lock _emufutex_g_bit_lock
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#define g_bit_trylock _emufutex_g_bit_trylock
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#define g_bit_unlock _emufutex_g_bit_unlock
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#define g_pointer_bit_lock _emufutex_g_pointer_bit_lock
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#define g_pointer_bit_trylock _emufutex_g_pointer_bit_trylock
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#define g_pointer_bit_unlock _emufutex_g_pointer_bit_unlock
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#define _g_futex_thread_init _emufutex_g_futex_thread_init
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#define G_BIT_LOCK_FORCE_FUTEX_EMULATION
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@ -41,24 +49,32 @@
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#include <glib/gbitlock.c>
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#endif
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#include <glib.h>
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volatile GThread *owners[LOCKS];
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volatile gint locks[LOCKS];
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volatile gpointer ptrs[LOCKS];
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volatile gint bits[LOCKS];
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static void
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acquire (int nr)
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acquire (int nr,
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gboolean use_pointers)
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{
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GThread *self;
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self = g_thread_self ();
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if (!g_bit_trylock (&locks[nr], bits[nr]))
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g_assert_cmpint (((gsize) ptrs) % 8, ==, 0);
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if (!(use_pointers ?
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g_pointer_bit_trylock (&ptrs[nr], bits[nr])
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: g_bit_trylock (&locks[nr], bits[nr])))
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{
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if (g_test_verbose ())
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g_print ("thread %p going to block on lock %d\n", self, nr);
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g_bit_lock (&locks[nr], bits[nr]);
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if (use_pointers)
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g_pointer_bit_lock (&ptrs[nr], bits[nr]);
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else
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g_bit_lock (&locks[nr], bits[nr]);
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}
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g_assert (owners[nr] == NULL); /* hopefully nobody else is here */
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@ -71,23 +87,34 @@ acquire (int nr)
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g_assert (owners[nr] == self); /* hopefully this is still us... */
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owners[nr] = NULL; /* make way for the next guy */
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g_bit_unlock (&locks[nr], bits[nr]);
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if (use_pointers)
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g_pointer_bit_unlock (&ptrs[nr], bits[nr]);
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else
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g_bit_unlock (&locks[nr], bits[nr]);
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}
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static gpointer
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thread_func (gpointer data)
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{
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gboolean use_pointers = GPOINTER_TO_INT (data);
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gint i;
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GRand *rand;
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rand = g_rand_new ();
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for (i = 0; i < ITERATIONS; i++)
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acquire (g_random_int () % LOCKS);
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acquire (g_rand_int_range (rand, 0, LOCKS), use_pointers);
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g_rand_free (rand);
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return NULL;
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}
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static void
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testcase (void)
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testcase (gconstpointer data)
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{
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gboolean use_pointers = GPOINTER_TO_INT (data);
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GThread *threads[THREADS];
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int i;
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@ -109,7 +136,9 @@ testcase (void)
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bits[i] = g_random_int () % 32;
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for (i = 0; i < THREADS; i++)
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threads[i] = g_thread_create (thread_func, NULL, TRUE, NULL);
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threads[i] = g_thread_create (thread_func,
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GINT_TO_POINTER (use_pointers),
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TRUE, NULL);
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for (i = 0; i < THREADS; i++)
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g_thread_join (threads[i]);
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@ -126,7 +155,8 @@ main (int argc, char **argv)
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{
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g_test_init (&argc, &argv, NULL);
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g_test_add_func ("/glib/1bit-mutex" SUFFIX, testcase);
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g_test_add_data_func ("/glib/1bit-mutex" SUFFIX "/int", (gpointer) 0, testcase);
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g_test_add_data_func ("/glib/1bit-mutex" SUFFIX "/pointer", (gpointer) 1, testcase);
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return g_test_run ();
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}
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