server-skynet-source-3rd-je.../include/jemalloc/internal/ticker.h
David T. Goldblatt dd7e283b6f Tweak the ticker paths to help GCC generate better code.
GCC on its own isn't quite able to turn the ticker subtract into a memory
operation followed by a js.
2018-02-21 16:04:23 -08:00

79 lines
2.0 KiB
C

#ifndef JEMALLOC_INTERNAL_TICKER_H
#define JEMALLOC_INTERNAL_TICKER_H
#include "jemalloc/internal/util.h"
/**
* A ticker makes it easy to count-down events until some limit. You
* ticker_init the ticker to trigger every nticks events. You then notify it
* that an event has occurred with calls to ticker_tick (or that nticks events
* have occurred with a call to ticker_ticks), which will return true (and reset
* the counter) if the countdown hit zero.
*/
typedef struct {
int32_t tick;
int32_t nticks;
} ticker_t;
static inline void
ticker_init(ticker_t *ticker, int32_t nticks) {
ticker->tick = nticks;
ticker->nticks = nticks;
}
static inline void
ticker_copy(ticker_t *ticker, const ticker_t *other) {
*ticker = *other;
}
static inline int32_t
ticker_read(const ticker_t *ticker) {
return ticker->tick;
}
/*
* Not intended to be a public API. Unfortunately, on x86, neither gcc nor
* clang seems smart enough to turn
* ticker->tick -= nticks;
* if (unlikely(ticker->tick < 0)) {
* fixup ticker
* return true;
* }
* return false;
* into
* subq %nticks_reg, (%ticker_reg)
* js fixup ticker
*
* unless we force "fixup ticker" out of line. In that case, gcc gets it right,
* but clang now does worse than before. So, on x86 with gcc, we force it out
* of line, but otherwise let the inlining occur. Ordinarily this wouldn't be
* worth the hassle, but this is on the fast path of both malloc and free (via
* tcache_event).
*/
#if defined(__GNUC__) && !defined(__clang__) \
&& (defined(__x86_64__) || defined(__i386__))
JEMALLOC_NOINLINE
#endif
static bool
ticker_fixup(ticker_t *ticker) {
ticker->tick = ticker->nticks;
return true;
}
static inline bool
ticker_ticks(ticker_t *ticker, int32_t nticks) {
ticker->tick -= nticks;
if (unlikely(ticker->tick < 0)) {
return ticker_fixup(ticker);
}
return false;
}
static inline bool
ticker_tick(ticker_t *ticker) {
return ticker_ticks(ticker, 1);
}
#endif /* JEMALLOC_INTERNAL_TICKER_H */