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Simplify IO_CACHE by removing current_pos and end_pos as self-references

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These self references were previously used to avoid having to check the
IO_CACHE's type. However, a benchmark shows that on x86 5930k stock,
the type comparison is marginally faster than the double pointer dereference.
For 40 billion my_b_tell calls, the difference is .1 seconds in favor of performing the
type check. (Basically there is no measurable difference)

To prevent bugs from copying the structure using the equals(=) operator,
and having to do the bookkeeping manually, remove these "convenience"
variables.
This commit is contained in:
Vicențiu Ciorbaru 2017-06-18 19:48:57 +03:00
commit 9003869390
6 changed files with 11 additions and 57 deletions
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20
include/my_sys.h
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@ -422,14 +422,6 @@ typedef struct st_io_cache /* Used when cacheing files */
/* The non-inclusive boundary of the valid write area */
uchar *write_end;
/*
Current_pos and current_end are convenience variables used by
my_b_tell() and other routines that need to know the current offset
current_pos points to &write_pos, and current_end to &write_end in a
WRITE_CACHE, and &read_pos and &read_end respectively otherwise
*/
uchar **current_pos, **current_end;
/*
The lock is for append buffer used in SEQ_READ_APPEND cache
need mutex copying from append buffer to read buffer.
@ -584,7 +576,11 @@ static inline size_t my_b_fill(IO_CACHE *info)
static inline my_off_t my_b_tell(const IO_CACHE *info)
{
return info->pos_in_file + (*info->current_pos - info->request_pos);
if (info->type == WRITE_CACHE) {
return info->pos_in_file + (info->write_pos - info->request_pos);
}
return info->pos_in_file + (info->read_pos - info->request_pos);
}
static inline my_off_t my_b_write_tell(const IO_CACHE *info)
@ -609,7 +605,10 @@ static inline my_off_t my_b_get_pos_in_file(const IO_CACHE *info)
static inline size_t my_b_bytes_in_cache(const IO_CACHE *info)
{
return *info->current_end - *info->current_pos;
if (info->type == WRITE_CACHE) {
return info->write_end - info->write_pos;
}
return info->read_end - info->read_pos;
}
int my_b_copy_to_file(IO_CACHE *cache, FILE *file);
@ -803,7 +802,6 @@ extern int init_io_cache(IO_CACHE *info,File file,size_t cachesize,
extern my_bool reinit_io_cache(IO_CACHE *info,enum cache_type type,
my_off_t seek_offset, my_bool use_async_io,
my_bool clear_cache);
extern void setup_io_cache(IO_CACHE* info);
extern void init_io_cache_share(IO_CACHE *read_cache, IO_CACHE_SHARE *cshare,
IO_CACHE *write_cache, uint num_threads);