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PRNG: Remove atomic functionality.

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These had no uses and complicated the API.  As a rule we now expect to only use
thread-local randomization for contention-reduction reasons, so we only pay the
API costs and never get the functionality benefits.
This commit is contained in:
David Goldblatt 2020-08-14 09:17:11 -07:00 committed by David Goldblatt
parent 0513047170
commit 9e6aa77ab9
2 changed files with 71 additions and 94 deletions
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81
include/jemalloc/internal/prng.h
View File

@ -1,7 +1,6 @@
#ifndef JEMALLOC_INTERNAL_PRNG_H
#define JEMALLOC_INTERNAL_PRNG_H
#include "jemalloc/internal/atomic.h"
#include "jemalloc/internal/bit_util.h"
/*
@ -59,66 +58,38 @@ prng_state_next_zu(size_t state) {
/*
* The prng_lg_range functions give a uniform int in the half-open range [0,
* 2**lg_range). If atomic is true, they do so safely from multiple threads.
* Multithreaded 64-bit prngs aren't supported.
* 2**lg_range).
*/
JEMALLOC_ALWAYS_INLINE uint32_t
prng_lg_range_u32(atomic_u32_t *state, unsigned lg_range, bool atomic) {
uint32_t ret, state0, state1;
prng_lg_range_u32(uint32_t *state, unsigned lg_range) {
assert(lg_range > 0);
assert(lg_range <= 32);
state0 = atomic_load_u32(state, ATOMIC_RELAXED);
if (atomic) {
do {
state1 = prng_state_next_u32(state0);
} while (!atomic_compare_exchange_weak_u32(state, &state0,
state1, ATOMIC_RELAXED, ATOMIC_RELAXED));
} else {
state1 = prng_state_next_u32(state0);
atomic_store_u32(state, state1, ATOMIC_RELAXED);
}
ret = state1 >> (32 - lg_range);
*state = prng_state_next_u32(*state);
uint32_t ret = *state >> (32 - lg_range);
return ret;
}
JEMALLOC_ALWAYS_INLINE uint64_t
prng_lg_range_u64(uint64_t *state, unsigned lg_range) {
uint64_t ret, state1;
assert(lg_range > 0);
assert(lg_range <= 64);
state1 = prng_state_next_u64(*state);
*state = state1;
ret = state1 >> (64 - lg_range);
*state = prng_state_next_u64(*state);
uint64_t ret = *state >> (64 - lg_range);
return ret;
}
JEMALLOC_ALWAYS_INLINE size_t
prng_lg_range_zu(atomic_zu_t *state, unsigned lg_range, bool atomic) {
size_t ret, state0, state1;
prng_lg_range_zu(size_t *state, unsigned lg_range) {
assert(lg_range > 0);
assert(lg_range <= ZU(1) << (3 + LG_SIZEOF_PTR));
state0 = atomic_load_zu(state, ATOMIC_RELAXED);
if (atomic) {
do {
state1 = prng_state_next_zu(state0);
} while (atomic_compare_exchange_weak_zu(state, &state0,
state1, ATOMIC_RELAXED, ATOMIC_RELAXED));
} else {
state1 = prng_state_next_zu(state0);
atomic_store_zu(state, state1, ATOMIC_RELAXED);
}
ret = state1 >> ((ZU(1) << (3 + LG_SIZEOF_PTR)) - lg_range);
*state = prng_state_next_zu(*state);
size_t ret = *state >> ((ZU(1) << (3 + LG_SIZEOF_PTR)) - lg_range);
return ret;
}
@ -129,20 +100,24 @@ prng_lg_range_zu(atomic_zu_t *state, unsigned lg_range, bool atomic) {
*/
JEMALLOC_ALWAYS_INLINE uint32_t
prng_range_u32(atomic_u32_t *state, uint32_t range, bool atomic) {
uint32_t ret;
unsigned lg_range;
prng_range_u32(uint32_t *state, uint32_t range) {
assert(range != 0);
/*
* If range were 1, lg_range would be 0, so the shift in
* prng_lg_range_u32 would be a shift of a 32-bit variable by 32 bits,
* which is UB. Just handle this case as a one-off.
*/
if (range == 1) {
return 0;
}
/* Compute the ceiling of lg(range). */
lg_range = ffs_u32(pow2_ceil_u32(range));
unsigned lg_range = ffs_u32(pow2_ceil_u32(range));
/* Generate a result in [0..range) via repeated trial. */
uint32_t ret;
do {
ret = prng_lg_range_u32(state, lg_range, atomic);
ret = prng_lg_range_u32(state, lg_range);
} while (ret >= range);
return ret;
@ -150,17 +125,18 @@ prng_range_u32(atomic_u32_t *state, uint32_t range, bool atomic) {
JEMALLOC_ALWAYS_INLINE uint64_t
prng_range_u64(uint64_t *state, uint64_t range) {
uint64_t ret;
unsigned lg_range;
assert(range != 0);
/* See the note in prng_range_u32. */
if (range == 1) {
return 0;
}
/* Compute the ceiling of lg(range). */
lg_range = ffs_u64(pow2_ceil_u64(range));
unsigned lg_range = ffs_u64(pow2_ceil_u64(range));
/* Generate a result in [0..range) via repeated trial. */
uint64_t ret;
do {
ret = prng_lg_range_u64(state, lg_range);
} while (ret >= range);
@ -169,20 +145,21 @@ prng_range_u64(uint64_t *state, uint64_t range) {
}
JEMALLOC_ALWAYS_INLINE size_t
prng_range_zu(atomic_zu_t *state, size_t range, bool atomic) {
size_t ret;
unsigned lg_range;
prng_range_zu(size_t *state, size_t range) {
assert(range != 0);
/* See the note in prng_range_u32. */
if (range == 1) {
return 0;
}
/* Compute the ceiling of lg(range). */
lg_range = ffs_u64(pow2_ceil_u64(range));
unsigned lg_range = ffs_u64(pow2_ceil_u64(range));
/* Generate a result in [0..range) via repeated trial. */
size_t ret;
do {
ret = prng_lg_range_zu(state, lg_range, atomic);
ret = prng_lg_range_zu(state, lg_range);
} while (ret >= range);
return ret;

84
test/unit/prng.c
View File

@ -1,34 +1,34 @@
#include "test/jemalloc_test.h"
static void
test_prng_lg_range_u32(bool atomic) {
atomic_u32_t sa, sb;
test_prng_lg_range_u32() {
uint32_t sa, sb;
uint32_t ra, rb;
unsigned lg_range;
atomic_store_u32(&sa, 42, ATOMIC_RELAXED);
ra = prng_lg_range_u32(&sa, 32, atomic);
atomic_store_u32(&sa, 42, ATOMIC_RELAXED);
rb = prng_lg_range_u32(&sa, 32, atomic);
sa = 42;
ra = prng_lg_range_u32(&sa, 32);
sa = 42;
rb = prng_lg_range_u32(&sa, 32);
expect_u32_eq(ra, rb,
"Repeated generation should produce repeated results");
atomic_store_u32(&sb, 42, ATOMIC_RELAXED);
rb = prng_lg_range_u32(&sb, 32, atomic);
sb = 42;
rb = prng_lg_range_u32(&sb, 32);
expect_u32_eq(ra, rb,
"Equivalent generation should produce equivalent results");
atomic_store_u32(&sa, 42, ATOMIC_RELAXED);
ra = prng_lg_range_u32(&sa, 32, atomic);
rb = prng_lg_range_u32(&sa, 32, atomic);
sa = 42;
ra = prng_lg_range_u32(&sa, 32);
rb = prng_lg_range_u32(&sa, 32);
expect_u32_ne(ra, rb,
"Full-width results must not immediately repeat");
atomic_store_u32(&sa, 42, ATOMIC_RELAXED);
ra = prng_lg_range_u32(&sa, 32, atomic);
sa = 42;
ra = prng_lg_range_u32(&sa, 32);
for (lg_range = 31; lg_range > 0; lg_range--) {
atomic_store_u32(&sb, 42, ATOMIC_RELAXED);
rb = prng_lg_range_u32(&sb, lg_range, atomic);
sb = 42;
rb = prng_lg_range_u32(&sb, lg_range);
expect_u32_eq((rb & (UINT32_C(0xffffffff) << lg_range)),
0, "High order bits should be 0, lg_range=%u", lg_range);
expect_u32_eq(rb, (ra >> (32 - lg_range)),
@ -74,35 +74,35 @@ test_prng_lg_range_u64(void) {
}
static void
test_prng_lg_range_zu(bool atomic) {
atomic_zu_t sa, sb;
test_prng_lg_range_zu() {
size_t sa, sb;
size_t ra, rb;
unsigned lg_range;
atomic_store_zu(&sa, 42, ATOMIC_RELAXED);
ra = prng_lg_range_zu(&sa, ZU(1) << (3 + LG_SIZEOF_PTR), atomic);
atomic_store_zu(&sa, 42, ATOMIC_RELAXED);
rb = prng_lg_range_zu(&sa, ZU(1) << (3 + LG_SIZEOF_PTR), atomic);
sa = 42;
ra = prng_lg_range_zu(&sa, ZU(1) << (3 + LG_SIZEOF_PTR));
sa = 42;
rb = prng_lg_range_zu(&sa, ZU(1) << (3 + LG_SIZEOF_PTR));
expect_zu_eq(ra, rb,
"Repeated generation should produce repeated results");
atomic_store_zu(&sb, 42, ATOMIC_RELAXED);
rb = prng_lg_range_zu(&sb, ZU(1) << (3 + LG_SIZEOF_PTR), atomic);
sb = 42;
rb = prng_lg_range_zu(&sb, ZU(1) << (3 + LG_SIZEOF_PTR));
expect_zu_eq(ra, rb,
"Equivalent generation should produce equivalent results");
atomic_store_zu(&sa, 42, ATOMIC_RELAXED);
ra = prng_lg_range_zu(&sa, ZU(1) << (3 + LG_SIZEOF_PTR), atomic);
rb = prng_lg_range_zu(&sa, ZU(1) << (3 + LG_SIZEOF_PTR), atomic);
sa = 42;
ra = prng_lg_range_zu(&sa, ZU(1) << (3 + LG_SIZEOF_PTR));
rb = prng_lg_range_zu(&sa, ZU(1) << (3 + LG_SIZEOF_PTR));
expect_zu_ne(ra, rb,
"Full-width results must not immediately repeat");
atomic_store_zu(&sa, 42, ATOMIC_RELAXED);
ra = prng_lg_range_zu(&sa, ZU(1) << (3 + LG_SIZEOF_PTR), atomic);
sa = 42;
ra = prng_lg_range_zu(&sa, ZU(1) << (3 + LG_SIZEOF_PTR));
for (lg_range = (ZU(1) << (3 + LG_SIZEOF_PTR)) - 1; lg_range > 0;
lg_range--) {
atomic_store_zu(&sb, 42, ATOMIC_RELAXED);
rb = prng_lg_range_zu(&sb, lg_range, atomic);
sb = 42;
rb = prng_lg_range_zu(&sb, lg_range);
expect_zu_eq((rb & (SIZE_T_MAX << lg_range)),
0, "High order bits should be 0, lg_range=%u", lg_range);
expect_zu_eq(rb, (ra >> ((ZU(1) << (3 + LG_SIZEOF_PTR)) -
@ -112,12 +112,12 @@ test_prng_lg_range_zu(bool atomic) {
}
TEST_BEGIN(test_prng_lg_range_u32_nonatomic) {
test_prng_lg_range_u32(false);
test_prng_lg_range_u32();
}
TEST_END
TEST_BEGIN(test_prng_lg_range_u32_atomic) {
test_prng_lg_range_u32(true);
test_prng_lg_range_u32();
}
TEST_END
@ -127,29 +127,29 @@ TEST_BEGIN(test_prng_lg_range_u64_nonatomic) {
TEST_END
TEST_BEGIN(test_prng_lg_range_zu_nonatomic) {
test_prng_lg_range_zu(false);
test_prng_lg_range_zu();
}
TEST_END
TEST_BEGIN(test_prng_lg_range_zu_atomic) {
test_prng_lg_range_zu(true);
test_prng_lg_range_zu();
}
TEST_END
static void
test_prng_range_u32(bool atomic) {
test_prng_range_u32() {
uint32_t range;
#define MAX_RANGE 10000000
#define RANGE_STEP 97
#define NREPS 10
for (range = 2; range < MAX_RANGE; range += RANGE_STEP) {
atomic_u32_t s;
uint32_t s;
unsigned rep;
atomic_store_u32(&s, range, ATOMIC_RELAXED);
s = range;
for (rep = 0; rep < NREPS; rep++) {
uint32_t r = prng_range_u32(&s, range, atomic);
uint32_t r = prng_range_u32(&s, range);
expect_u32_lt(r, range, "Out of range");
}
@ -177,19 +177,19 @@ test_prng_range_u64(void) {
}
static void
test_prng_range_zu(bool atomic) {
test_prng_range_zu() {
size_t range;
#define MAX_RANGE 10000000
#define RANGE_STEP 97
#define NREPS 10
for (range = 2; range < MAX_RANGE; range += RANGE_STEP) {
atomic_zu_t s;
size_t s;
unsigned rep;
atomic_store_zu(&s, range, ATOMIC_RELAXED);
s = range;
for (rep = 0; rep < NREPS; rep++) {
size_t r = prng_range_zu(&s, range, atomic);
size_t r = prng_range_zu(&s, range);
expect_zu_lt(r, range, "Out of range");
}