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LibretroAdmin
2b4bc98676
The shader backends read gyro, accelerometer and rest each frame from the video thread. They were published under a seqlock, whose reader started over - spinning - while the poll was mid-publication, and whose nine floats went through nine atomic stores and loads. They are now three slots of nine floats: the poll writes its own and hands it over with one exchange for the middle slot; the reader, when the middle is new, exchanges its slot for it and reads the floats where they lie. Neither side ever waits or retries, and a read never mixes two polls. The exchange lives in input_sensor_snap.h so a test can drive the same code. sensor_snap_test publishes as fast as it can from one thread while another reads, and checks no read is mixed or goes backwards and the newest is read once the writer stops; CI runs it under ASan, TSan and Wine. The frontend harness's idle lane counts publications instead of the sequence.
79 lines
2.8 KiB
C
79 lines
2.8 KiB
C
/* RetroArch - A frontend for libretro.
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*
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* RetroArch is free software: you can redistribute it and/or modify it under the terms
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* of the GNU General Public License as published by the Free Software Found-
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* ation, either version 3 of the License, or (at your option) any later version.
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*
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* RetroArch is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
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* without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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* PURPOSE. See the GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along with RetroArch.
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* If not, see <http://www.gnu.org/licenses/>.
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*/
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/* The sensor snapshot the shader backends read each frame, from the
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* video thread: gyro, accelerometer and rest, nine floats to a slot.
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*
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* Three slots - the poll writes one, the reader reads one, the newest
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* waits in the middle - handed over by an exchange of @middle, so
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* neither side ever waits and a read never mixes two publications. One
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* writer and one reader. A header of its own so that a test can drive
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* the very same code.
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*
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* The indices are kept so that the zeroed state is a valid one: the
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* middle slot is the stored value ^ 1, the reader's ^ 2. */
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#ifndef __INPUT_SENSOR_SNAP_H
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#define __INPUT_SENSOR_SNAP_H
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#include <string.h>
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#include <stdint.h>
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#include <retro_inline.h>
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#include <retro_atomic.h>
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#define INPUT_SENSOR_SNAP_FRESH 4
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typedef struct input_sensor_snap
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{
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float slot[3][9];
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retro_atomic_int_t middle;
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uint8_t write; /* the writer's */
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uint8_t read; /* the reader's */
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unsigned published; /* the writer's: how many */
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} input_sensor_snap_t;
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static INLINE void input_sensor_snap_publish(input_sensor_snap_t *s,
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const float *gyro3, const float *accel3, const float *rest3)
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{
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unsigned w = s->write;
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float *dst = s->slot[w];
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memcpy(dst, gyro3, 3 * sizeof(float));
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memcpy(dst + 3, accel3, 3 * sizeof(float));
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memcpy(dst + 6, rest3, 3 * sizeof(float));
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s->write = (uint8_t)(((unsigned)retro_atomic_exchange_int(&s->middle,
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(int)((w ^ 1u) | INPUT_SENSOR_SNAP_FRESH)) & 3u) ^ 1u);
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s->published++;
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}
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/* The newest published, taken in exchange for the slot last read and
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* read where it lies. */
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static INLINE void input_sensor_snap_take(input_sensor_snap_t *s,
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float *gyro3, float *accel3, float *rest3)
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{
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unsigned r = s->read ^ 2u;
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const float *v;
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if (retro_atomic_load_acquire_int(&s->middle) & INPUT_SENSOR_SNAP_FRESH)
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{
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r = ((unsigned)retro_atomic_exchange_int(&s->middle,
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(int)(r ^ 1u)) & 3u) ^ 1u;
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s->read = (uint8_t)(r ^ 2u);
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}
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v = s->slot[r];
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memcpy(gyro3, v, 3 * sizeof(float));
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memcpy(accel3, v + 3, 3 * sizeof(float));
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memcpy(rest3, v + 6, 3 * sizeof(float));
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}
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#endif
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