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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
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@@ -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;