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server: fix race condition in lz global dictionary, in its image segments list

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This commit is contained in:
Yonit Halperin 2010-04-09 10:09:47 +02:00 committed by Alexander Larsson
parent 22d1ac9eb5
commit a3700a1bfb
1 changed files with 34 additions and 21 deletions
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55
server/glz_encoder_dictionary.c
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@ -332,7 +332,7 @@ static WindowImage *__glz_dictionary_window_alloc_image(SharedDictionary *dict)
return ret;
}
/* NOTE - it also updates the used_segs_list*/
/* NOTE - it doesn't update the used_segs list*/
static uint32_t __glz_dictionary_window_alloc_image_seg(SharedDictionary *dict)
{
uint32_t seg_id;
@ -349,18 +349,6 @@ static uint32_t __glz_dictionary_window_alloc_image_seg(SharedDictionary *dict)
seg = dict->window.segs + seg_id;
dict->window.free_segs_head = seg->next;
// first segment
if (dict->window.used_segs_tail == NULL_IMAGE_SEG_ID) {
dict->window.used_segs_head = seg_id;
dict->window.used_segs_tail = seg_id;
} else {
int prev_tail = dict->window.used_segs_tail;
dict->window.segs[prev_tail].next = seg_id;
dict->window.used_segs_tail = seg_id;
}
seg->next = NULL_IMAGE_SEG_ID;
return seg_id;
}
@ -467,9 +455,9 @@ static void glz_dictionary_window_remove_head(SharedDictionary *dict, uint32_t e
}
}
static uint32_t glz_dictionary_window_add_image_seg(SharedDictionary *dict, WindowImage* image,
int size, int stride,
uint8_t *lines, unsigned int num_lines)
static uint32_t glz_dictionary_window_alloc_image_seg(SharedDictionary *dict, WindowImage* image,
int size, int stride,
uint8_t *lines, unsigned int num_lines)
{
uint32_t seg_id = __glz_dictionary_window_alloc_image_seg(dict);
WindowImageSegment *seg = &dict->window.segs[seg_id];
@ -481,6 +469,8 @@ static uint32_t glz_dictionary_window_add_image_seg(SharedDictionary *dict, Wind
seg->pixels_so_far = dict->window.pixels_so_far;
dict->window.pixels_so_far += seg->pixels_num;
seg->next = NULL_IMAGE_SEG_ID;
return seg_id;
}
@ -492,7 +482,7 @@ static WindowImage *glz_dictionary_window_add_image(SharedDictionary *dict, LzIm
{
unsigned int num_lines = num_first_lines;
unsigned int row;
uint32_t seg_id;
uint32_t seg_id, prev_seg_id;
uint8_t* lines = first_lines;
// alloc image info,update used head tail, if used_head null - update head
WindowImage *image = __glz_dictionary_window_alloc_image(dict);
@ -509,13 +499,16 @@ static WindowImage *glz_dictionary_window_add_image(SharedDictionary *dict, LzIm
}
for (row = 0;;) {
seg_id = glz_dictionary_window_add_image_seg(dict, image,
image_size * num_lines / image_height,
image_stride,
lines, num_lines);
seg_id = glz_dictionary_window_alloc_image_seg(dict, image,
image_size * num_lines / image_height,
image_stride,
lines, num_lines);
if (row == 0) {
image->first_seg = seg_id;
} else {
dict->window.segs[prev_seg_id].next = seg_id;
}
row += num_lines;
if (row < (uint32_t)image_height) {
num_lines = dict->cur_usr->more_lines(dict->cur_usr, &lines);
@ -525,6 +518,26 @@ static WindowImage *glz_dictionary_window_add_image(SharedDictionary *dict, LzIm
} else {
break;
}
prev_seg_id = seg_id;
}
if (dict->window.used_segs_tail == NULL_IMAGE_SEG_ID) {
dict->window.used_segs_head = image->first_seg;
dict->window.used_segs_tail = seg_id;
} else {
int prev_tail = dict->window.used_segs_tail;
// The used segs may be in use by another thread which is during encoding
// (read-only use - when going over the segs of an image,
// see glz_encode_tmpl::compress).
// Thus, the 'next' field of the list's tail can be accessed only
// after all the new tail's data was set. Note that we are relying on
// an atomic assignment (32 bit varaible).
// For the other thread that may read 'next' of the old tail, NULL_IMAGE_SEG_ID
// is equivalent to a segment with an image id that is different
// from the image id of the tail, so we don't need to further protect this field.
dict->window.segs[prev_tail].next = image->first_seg;
dict->window.used_segs_tail = seg_id;
}
image->is_alive = TRUE;