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libsysprof-capture: sleep and try again to get an event

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Unless we've failed before, then just bail immediately so that applications
which loose their controller keep running with minimal overhead.
This commit is contained in:
Christian Hergert
2023-08-15 15:37:24 -07:00
parent b96bf5c969
commit c45aba997d
1 changed files with 28 additions and 17 deletions
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45
src/libsysprof-capture/mapped-ring-buffer.c
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@ -69,6 +69,7 @@ struct _MappedRingBuffer
void *map;
size_t body_size;
size_t page_size;
unsigned has_failed : 1;
};
static inline MappedRingHeader *
@ -405,27 +406,37 @@ mapped_ring_buffer_allocate (MappedRingBuffer *self,
assert (length < self->body_size);
assert ((length & 0x7) == 0);
header = get_header (self);
__atomic_load (&header->head, &headpos, __ATOMIC_SEQ_CST);
__atomic_load (&header->tail, &tailpos, __ATOMIC_SEQ_CST);
for (unsigned i = 0; i < 1000; i++)
{
header = get_header (self);
__atomic_load (&header->head, &headpos, __ATOMIC_SEQ_CST);
__atomic_load (&header->tail, &tailpos, __ATOMIC_SEQ_CST);
/* We need to check that there is enough space for @length at the
* current position in the write buffer. We cannot fully catch up
* to head, we must be at least one byte short of it. If we do not
* have enough space, then return NULL.
*
* When we have finished writing our frame data, we will push the tail
* forward with an atomic write.
*/
/* We need to check that there is enough space for @length at the
* current position in the write buffer. We cannot fully catch up
* to head, we must be at least one byte short of it. If we do not
* have enough space, then return NULL.
*
* When we have finished writing our frame data, we will push the tail
* forward with an atomic write.
*/
if (tailpos == headpos)
return get_body_at_pos (self, tailpos);
if (tailpos == headpos)
return get_body_at_pos (self, tailpos);
if (headpos < tailpos)
headpos += self->body_size;
if (headpos < tailpos)
headpos += self->body_size;
if (tailpos + length < headpos)
return get_body_at_pos (self, tailpos);
if (tailpos + length < headpos)
return get_body_at_pos (self, tailpos);
if (self->has_failed)
break;
usleep (1000); /* 1 msec */
}
self->has_failed = true;
return NULL;
}