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/cvs/libev/ev_linuxaio.c
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Comparing libev/ev_linuxaio.c (file contents):
Revision 1.12 by root, Sun Jun 23 23:02:09 2019 UTC vs.
Revision 1.13 by root, Sun Jun 23 23:38:38 2019 UTC

… …
219static int 219static int
220linuxaio_get_events_from_ring (EV_P) 220linuxaio_get_events_from_ring (EV_P)
221{ 221{
222 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx; 222 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
223 223
224 unsigned head = ring->head; 224 /* the kernel reads and writes both of these variables, */
225 /* as a C extension, we assume that volatile use here */
226 /* both makes reads atomic and once-only */
227 unsigned head = *(volatile unsigned *)&ring->head;
225 unsigned tail = *(volatile unsigned *)&ring->tail; 228 unsigned tail = *(volatile unsigned *)&ring->tail;
226 229
227 if (head == tail) 230 if (head == tail)
228 return 0; 231 return 0;
229 232
… …
243 { 246 {
244 linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head); 247 linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head);
245 linuxaio_parse_events (EV_A_ ring->io_events, tail); 248 linuxaio_parse_events (EV_A_ ring->io_events, tail);
246 } 249 }
247 250
251 /* as an extension to C, we hope that the volatile will makethis atomic and once-only */
248 *(volatile unsigned *)&ring->head = tail; 252 *(volatile unsigned *)&ring->head = tail;
249 /* make sure kernel can see our new head value - probably not required */ 253 /* make sure kernel can see our new head value - probably not required */
250 ECB_MEMORY_FENCE_RELEASE; 254 ECB_MEMORY_FENCE_RELEASE;
251 255
252 return 1; 256 return 1;

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