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gbitlock: Drop unnecessary volatile qualifiers
This follows on from !1719. It drops volatile qualifiers on internal functions in `gbitlock.c`, and casts volatile public arguments to non-volatile versions to avoid the `g_atomic_*()` macros from propagating the volatile qualifier. We can’t drop the `volatile` qualifier from the public API in `gbitlock.h`, as that would unfortunately be an API break. Update the documentation in `gbitlock` to mention that users of the API should not use `volatile`. See http://c.isvolatileusefulwiththreads.com/ Signed-off-by: Philip Withnall <pwithnall@endlessos.org> Fixes: #2418
This commit is contained in:
Philip Withnall
parent
91759dbd63
commit
11cd751203
@ -76,8 +76,8 @@ static GSList *g_futex_address_list = NULL;
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* separate process.
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*/
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static void
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g_futex_wait (const volatile gint *address,
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gint value)
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g_futex_wait (const gint *address,
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gint value)
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{
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syscall (__NR_futex, address, (gsize) FUTEX_WAIT_PRIVATE, (gsize) value, NULL);
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}
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@ -94,7 +94,7 @@ g_futex_wait (const volatile gint *address,
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* thread being woken up.
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*/
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static void
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g_futex_wake (const volatile gint *address)
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g_futex_wake (const gint *address)
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{
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syscall (__NR_futex, address, (gsize) FUTEX_WAKE_PRIVATE, (gsize) 1, NULL);
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}
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@ -104,13 +104,13 @@ g_futex_wake (const volatile gint *address)
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/* emulate futex(2) */
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typedef struct
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{
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const volatile gint *address;
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gint ref_count;
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GCond wait_queue;
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const gint *address;
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gint ref_count;
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GCond wait_queue;
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} WaitAddress;
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static WaitAddress *
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g_futex_find_address (const volatile gint *address)
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g_futex_find_address (const gint *address)
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{
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GSList *node;
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@ -126,8 +126,8 @@ g_futex_find_address (const volatile gint *address)
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}
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static void
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g_futex_wait (const volatile gint *address,
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gint value)
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g_futex_wait (const gint *address,
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gint value)
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{
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g_mutex_lock (&g_futex_mutex);
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if G_LIKELY (g_atomic_int_get (address) == value)
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@ -159,7 +159,7 @@ g_futex_wait (const volatile gint *address,
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}
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static void
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g_futex_wake (const volatile gint *address)
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g_futex_wake (const gint *address)
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{
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WaitAddress *waiter;
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@ -177,7 +177,7 @@ g_futex_wake (const volatile gint *address)
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#endif
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#define CONTENTION_CLASSES 11
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static volatile gint g_bit_lock_contended[CONTENTION_CLASSES];
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static gint g_bit_lock_contended[CONTENTION_CLASSES]; /* (atomic) */
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#if (defined (i386) || defined (__amd64__))
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#if G_GNUC_CHECK_VERSION(4, 5)
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@ -202,7 +202,8 @@ static volatile gint g_bit_lock_contended[CONTENTION_CLASSES];
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*
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* This function accesses @address atomically. All other accesses to
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* @address must be atomic in order for this function to work
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* reliably.
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* reliably. While @address has a `volatile` qualifier, this is a historical
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* artifact and the argument passed to it should not be `volatile`.
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*
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* Since: 2.24
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**/
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@ -210,6 +211,8 @@ void
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g_bit_lock (volatile gint *address,
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gint lock_bit)
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{
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gint *address_nonvolatile = (gint *) address;
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#ifdef USE_ASM_GOTO
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retry:
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__asm__ volatile goto ("lock bts %1, (%0)\n"
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@ -225,13 +228,13 @@ g_bit_lock (volatile gint *address,
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guint mask = 1u << lock_bit;
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guint v;
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v = (guint) g_atomic_int_get (address);
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v = (guint) g_atomic_int_get (address_nonvolatile);
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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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guint class = ((gsize) address_nonvolatile) % 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 (address, v);
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g_futex_wait (address_nonvolatile, 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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@ -241,14 +244,14 @@ g_bit_lock (volatile gint *address,
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guint v;
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retry:
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v = g_atomic_int_or (address, mask);
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v = g_atomic_int_or (address_nonvolatile, 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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guint class = ((gsize) address_nonvolatile) % 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 (address, v);
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g_futex_wait (address_nonvolatile, 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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@ -272,7 +275,8 @@ g_bit_lock (volatile gint *address,
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*
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* This function accesses @address atomically. All other accesses to
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* @address must be atomic in order for this function to work
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* reliably.
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* reliably. While @address has a `volatile` qualifier, this is a historical
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* artifact and the argument passed to it should not be `volatile`.
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*
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* Returns: %TRUE if the lock was acquired
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*
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@ -294,10 +298,11 @@ g_bit_trylock (volatile gint *address,
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return result;
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#else
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gint *address_nonvolatile = (gint *) address;
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guint mask = 1u << lock_bit;
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guint v;
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v = g_atomic_int_or (address, mask);
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v = g_atomic_int_or (address_nonvolatile, mask);
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return ~v & mask;
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#endif
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@ -314,7 +319,8 @@ g_bit_trylock (volatile gint *address,
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*
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* This function accesses @address atomically. All other accesses to
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* @address must be atomic in order for this function to work
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* reliably.
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* reliably. While @address has a `volatile` qualifier, this is a historical
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* artifact and the argument passed to it should not be `volatile`.
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*
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* Since: 2.24
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**/
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@ -322,6 +328,8 @@ void
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g_bit_unlock (volatile gint *address,
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gint lock_bit)
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{
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gint *address_nonvolatile = (gint *) address;
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#ifdef USE_ASM_GOTO
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__asm__ volatile ("lock btr %1, (%0)"
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: /* no output */
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@ -330,14 +338,14 @@ g_bit_unlock (volatile gint *address,
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#else
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guint mask = 1u << lock_bit;
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g_atomic_int_and (address, ~mask);
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g_atomic_int_and (address_nonvolatile, ~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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guint class = ((gsize) address_nonvolatile) % 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 (address);
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g_futex_wake (address_nonvolatile);
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}
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}
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@ -366,10 +374,10 @@ g_bit_unlock (volatile gint *address,
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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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static const gint *
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g_futex_int_address (const void *address)
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{
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const volatile gint *int_address = address;
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const gint *int_address = address;
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/* this implementation makes these (reasonable) assumptions: */
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G_STATIC_ASSERT (G_BYTE_ORDER == G_LITTLE_ENDIAN ||
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@ -395,12 +403,17 @@ g_futex_int_address (const volatile void *address)
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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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* While @address has a `volatile` qualifier, this is a historical
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* artifact and the argument passed to it should not be `volatile`.
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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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void *address_nonvolatile = (void *) address;
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g_return_if_fail (lock_bit < 32);
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{
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@ -416,23 +429,23 @@ void
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contended:
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{
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volatile gsize *pointer_address = address;
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gsize *pointer_address = address_nonvolatile;
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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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guint class = ((gsize) address_nonvolatile) % 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_futex_wait (g_futex_int_address (address_nonvolatile), 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 *pointer_address = address_nonvolatile;
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gsize mask = 1u << lock_bit;
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gsize v;
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@ -441,10 +454,10 @@ void
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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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guint class = ((gsize) address_nonvolatile) % 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_futex_wait (g_futex_int_address (address_nonvolatile), (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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@ -464,6 +477,9 @@ void
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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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* While @address has a `volatile` qualifier, this is a historical
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* artifact and the argument passed to it should not be `volatile`.
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*
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* Returns: %TRUE if the lock was acquired
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*
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* Since: 2.30
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@ -487,7 +503,8 @@ gboolean
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return result;
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#else
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volatile gsize *pointer_address = address;
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void *address_nonvolatile = (void *) address;
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gsize *pointer_address = address_nonvolatile;
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gsize mask = 1u << lock_bit;
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gsize v;
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@ -511,12 +528,17 @@ gboolean
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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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* While @address has a `volatile` qualifier, this is a historical
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* artifact and the argument passed to it should not be `volatile`.
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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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void *address_nonvolatile = (void *) address;
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g_return_if_fail (lock_bit < 32);
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{
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@ -526,16 +548,16 @@ void
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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 *pointer_address = address_nonvolatile;
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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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guint class = ((gsize) address_nonvolatile) % 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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g_futex_wake (g_futex_int_address (address_nonvolatile));
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}
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}
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}
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