Commit df0b2088 authored by Allison Karlitskaya's avatar Allison Karlitskaya Committed by Matthias Clasen

Implement pointer sized bitlocks

Based on a patch from Alexander Larsson.

https://bugzilla.gnome.org/show_bug.cgi?id=651467
parent 1a80405a
......@@ -22,6 +22,7 @@
#include "gbitlock.h"
#include <glib/gmessages.h>
#include <glib/gatomic.h>
#include <glib/gslist.h>
#include <glib/gthread.h>
......@@ -334,3 +335,195 @@ g_bit_unlock (volatile gint *address,
g_futex_wake (address);
}
}
/* We emulate pointer-sized futex(2) because the kernel API only
* supports integers.
*
* We assume that the 'interesting' part is always the lower order bits.
* This assumption holds because pointer bitlocks are restricted to
* using the low order bits of the pointer as the lock.
*
* On 32 bits, there is nothing to do since the pointer size is equal to
* the integer size. On little endian the lower-order bits don't move,
* so do nothing. Only on 64bit big endian do we need to do a bit of
* pointer arithmetic: the low order bits are shifted by 4 bytes. We
* have a helper function that always does the right thing here.
*
* Since we always consider the low-order bits of the integer value, a
* simple cast from (gsize) to (guint) always takes care of that.
*
* After that, pointer-sized futex becomes as simple as:
*
* g_futex_wait (g_futex_int_address (address), (guint) value);
*
* and
*
* g_futex_wake (g_futex_int_address (int_address));
*/
static const volatile gint *
g_futex_int_address (const volatile void *address)
{
const volatile gint *int_address = address;
#if G_BYTE_ORDER == G_BIG_ENDIAN && GLIB_SIZEOF_VOID_P == 8
int_address++;
#endif
return int_address;
}
/**
* g_pointer_bit_lock:
* @address: a pointer to a #gpointer-sized value
* @lock_bit: a bit value between 0 and 31
*
* This is equivalent to g_bit_lock, but working on pointers (or other
* pointer-sized values).
*
* For portability reasons, you may only lock on the bottom 32 bits of
* the pointer.
*
* Since: 2.30
**/
void
(g_pointer_bit_lock) (volatile void *address,
gint lock_bit)
{
g_return_if_fail (lock_bit < 32);
{
#if defined (__GNUC__) && (defined (i386) || defined (__amd64__))
retry:
asm volatile goto ("lock bts %1, (%0)\n"
"jc %l[contended]"
: /* no output */
: "r" (address), "r" ((gsize) lock_bit)
: "cc", "memory"
: contended);
return;
contended:
{
volatile gsize *pointer_address = address;
gsize mask = 1u << lock_bit;
gsize v;
v = (gsize) g_atomic_pointer_get (pointer_address);
if (v & mask)
{
guint class = ((gsize) address) % G_N_ELEMENTS (g_bit_lock_contended);
g_atomic_int_add (&g_bit_lock_contended[class], +1);
g_futex_wait (g_futex_int_address (address), v);
g_atomic_int_add (&g_bit_lock_contended[class], -1);
}
}
goto retry;
#else
volatile gsize *pointer_address = address;
gsize mask = 1u << lock_bit;
gsize v;
retry:
v = g_atomic_pointer_or (pointer_address, mask);
if (v & mask)
/* already locked */
{
guint class = ((gsize) address) % G_N_ELEMENTS (g_bit_lock_contended);
g_atomic_int_add (&g_bit_lock_contended[class], +1);
g_futex_wait (g_futex_int_address (address), (guint) v);
g_atomic_int_add (&g_bit_lock_contended[class], -1);
goto retry;
}
#endif
}
}
/**
* g_pointer_bit_trylock:
* @address: a pointer to a #gpointer-sized value
* @lock_bit: a bit value between 0 and 31
* @returns: %TRUE if the lock was acquired
*
* This is equivalent to g_bit_trylock, but working on pointers (or
* other pointer-sized values).
*
* For portability reasons, you may only lock on the bottom 32 bits of
* the pointer.
*
* Since: 2.30
**/
gboolean
(g_pointer_bit_trylock) (volatile void *address,
gint lock_bit)
{
g_return_val_if_fail (lock_bit < 32, FALSE);
{
#if defined (__GNUC__) && (defined (i386) || defined (__amd64__))
gboolean result;
asm volatile ("lock bts %2, (%1)\n"
"setnc %%al\n"
"movzx %%al, %0"
: "=r" (result)
: "r" (address), "r" ((gsize) lock_bit)
: "cc", "memory");
return result;
#else
volatile gsize *pointer_address = address;
gsize mask = 1u << lock_bit;
gsize v;
g_return_val_if_fail (lock_bit < 32, FALSE);
v = g_atomic_pointer_or (pointer_address, mask);
return ~v & mask;
#endif
}
}
/**
* g_pointer_bit_unlock:
* @address: a pointer to a #gpointer-sized value
* @lock_bit: a bit value between 0 and 31
*
* This is equivalent to g_bit_unlock, but working on pointers (or other
* pointer-sized values).
*
* For portability reasons, you may only lock on the bottom 32 bits of
* the pointer.
*
* Since: 2.30
**/
void
(g_pointer_bit_unlock) (volatile void *address,
gint lock_bit)
{
g_return_if_fail (lock_bit < 32);
{
#if defined (__GNUC__) && (defined (i386) || defined (__amd64__))
asm volatile ("lock btr %1, (%0)"
: /* no output */
: "r" (address), "r" ((gsize) lock_bit)
: "cc", "memory");
#else
volatile gsize *pointer_address = address;
gsize mask = 1u << lock_bit;
g_atomic_pointer_and (pointer_address, ~mask);
#endif
{
guint class = ((gsize) address) % G_N_ELEMENTS (g_bit_lock_contended);
if (g_atomic_int_get (&g_bit_lock_contended[class]))
g_futex_wake (g_futex_int_address (address));
}
}
}
......@@ -38,6 +38,35 @@ gboolean g_bit_trylock (volatile gint *address,
void g_bit_unlock (volatile gint *address,
gint lock_bit);
void g_pointer_bit_lock (volatile void *address,
gint lock_bit);
gboolean g_pointer_bit_trylock (volatile void *address,
gint lock_bit);
void g_pointer_bit_unlock (volatile void *address,
gint lock_bit);
#ifdef __GNUC__
#define g_pointer_bit_lock(address, lock_bit) \
(G_GNUC_EXTENSION ({ \
G_STATIC_ASSERT (sizeof *(address) == sizeof (gpointer)); \
g_pointer_bit_lock ((address), (lock_bit)); \
}))
#define g_pointer_bit_trylock(address, lock_bit) \
(G_GNUC_EXTENSION ({ \
G_STATIC_ASSERT (sizeof *(address) == sizeof (gpointer)); \
g_pointer_bit_trylock ((address), (lock_bit)); \
}))
#define g_pointer_bit_unlock(address, lock_bit) \
(G_GNUC_EXTENSION ({ \
G_STATIC_ASSERT (sizeof *(address) == sizeof (gpointer)); \
g_pointer_bit_unlock ((address), (lock_bit)); \
}))
#endif
G_END_DECLS
#endif /* __G_BITLOCK_H_ */
......@@ -1065,6 +1065,9 @@ g_string_append_c
g_bit_lock
g_bit_trylock
g_bit_unlock
g_pointer_bit_lock
g_pointer_bit_trylock
g_pointer_bit_unlock
g_once_impl
g_once_init_enter_impl
g_once_init_leave
......
......@@ -18,6 +18,7 @@
#define ITERATIONS 10000
#define THREADS 100
#include <glib.h>
#if TEST_EMULATED_FUTEX
/* this is defined for the 1bit-mutex-emufutex test.
......@@ -31,9 +32,16 @@
/* rebuild gbitlock.c without futex support,
defining our own version of the g_bit_*lock symbols
*/
#undef g_pointer_bit_lock
#undef g_pointer_bit_trylock
#undef g_pointer_bit_unlock
#define g_bit_lock _emufutex_g_bit_lock
#define g_bit_trylock _emufutex_g_bit_trylock
#define g_bit_unlock _emufutex_g_bit_unlock
#define g_pointer_bit_lock _emufutex_g_pointer_bit_lock
#define g_pointer_bit_trylock _emufutex_g_pointer_bit_trylock
#define g_pointer_bit_unlock _emufutex_g_pointer_bit_unlock
#define _g_futex_thread_init _emufutex_g_futex_thread_init
#define G_BIT_LOCK_FORCE_FUTEX_EMULATION
......@@ -41,24 +49,32 @@
#include <glib/gbitlock.c>
#endif
#include <glib.h>
volatile GThread *owners[LOCKS];
volatile gint locks[LOCKS];
volatile gpointer ptrs[LOCKS];
volatile gint bits[LOCKS];
static void
acquire (int nr)
acquire (int nr,
gboolean use_pointers)
{
GThread *self;
self = g_thread_self ();
if (!g_bit_trylock (&locks[nr], bits[nr]))
g_assert_cmpint (((gsize) ptrs) % 8, ==, 0);
if (!(use_pointers ?
g_pointer_bit_trylock (&ptrs[nr], bits[nr])
: g_bit_trylock (&locks[nr], bits[nr])))
{
if (g_test_verbose ())
g_print ("thread %p going to block on lock %d\n", self, nr);
g_bit_lock (&locks[nr], bits[nr]);
if (use_pointers)
g_pointer_bit_lock (&ptrs[nr], bits[nr]);
else
g_bit_lock (&locks[nr], bits[nr]);
}
g_assert (owners[nr] == NULL); /* hopefully nobody else is here */
......@@ -71,23 +87,34 @@ acquire (int nr)
g_assert (owners[nr] == self); /* hopefully this is still us... */
owners[nr] = NULL; /* make way for the next guy */
g_bit_unlock (&locks[nr], bits[nr]);
if (use_pointers)
g_pointer_bit_unlock (&ptrs[nr], bits[nr]);
else
g_bit_unlock (&locks[nr], bits[nr]);
}
static gpointer
thread_func (gpointer data)
{
gboolean use_pointers = GPOINTER_TO_INT (data);
gint i;
GRand *rand;
rand = g_rand_new ();
for (i = 0; i < ITERATIONS; i++)
acquire (g_random_int () % LOCKS);
acquire (g_rand_int_range (rand, 0, LOCKS), use_pointers);
g_rand_free (rand);
return NULL;
}
static void
testcase (void)
testcase (gconstpointer data)
{
gboolean use_pointers = GPOINTER_TO_INT (data);
GThread *threads[THREADS];
int i;
......@@ -109,7 +136,9 @@ testcase (void)
bits[i] = g_random_int () % 32;
for (i = 0; i < THREADS; i++)
threads[i] = g_thread_create (thread_func, NULL, TRUE, NULL);
threads[i] = g_thread_create (thread_func,
GINT_TO_POINTER (use_pointers),
TRUE, NULL);
for (i = 0; i < THREADS; i++)
g_thread_join (threads[i]);
......@@ -126,7 +155,8 @@ main (int argc, char **argv)
{
g_test_init (&argc, &argv, NULL);
g_test_add_func ("/glib/1bit-mutex" SUFFIX, testcase);
g_test_add_data_func ("/glib/1bit-mutex" SUFFIX "/int", (gpointer) 0, testcase);
g_test_add_data_func ("/glib/1bit-mutex" SUFFIX "/pointer", (gpointer) 1, testcase);
return g_test_run ();
}
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