Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Optimize Windows contention performance #455

Closed
wants to merge 1 commit into from
Closed

Optimize Windows contention performance #455

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Jump to
Jump to file
Failed to load files.
Diff view
Diff view
3 changes: 0 additions & 3 deletions src/internal.h
View file
Open in desktop
Expand Up @@ -283,9 +283,6 @@ DISPATCH_EXPORT DISPATCH_NOTHROW void dispatch_atfork_child(void);
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#if defined(_WIN32)
#define _CRT_RAND_S
#endif
#include <stdlib.h>
#include <string.h>
#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
Expand Down
42 changes: 18 additions & 24 deletions src/shims/yield.h
View file
Open in desktop
Expand Up @@ -84,14 +84,18 @@
((DISPATCH_CONTENTION_SPINS_MIN) + ((DISPATCH_CONTENTION_SPINS_MAX) - \
(DISPATCH_CONTENTION_SPINS_MIN)) / 2)
#elif defined(_WIN32)
#define _dispatch_contention_spins() ({ \
unsigned int _value; \
rand_s(&_value); \
(_value & DISPATCH_CONTENTION_SPINS_MAX) | DISPATCH_CONTENTION_SPINS_MIN; })
// Use randomness to prevent threads from resonating at the same frequency and
// permanently contending. Windows doesn't provide rand_r(), so use a simple
// LCG. (msvcrt has rand_s(), but its security guarantees aren't optimal here.)
#define _dispatch_contention_spins() ({ \
static os_atomic(unsigned int) _seed = 1; \
unsigned int _next = os_atomic_load(&_seed, relaxed); \
os_atomic_store(&_seed, _next * 1103515245 + 12345, relaxed); \
((_next >> 24) & (DISPATCH_CONTENTION_SPINS_MAX)) | \
(DISPATCH_CONTENTION_SPINS_MIN); })
#else
// Use randomness to prevent threads from resonating at the same
// frequency and permanently contending. All threads sharing the same
// seed value is safe with the FreeBSD rand_r implementation.
// All threads sharing the same seed value is safe with the FreeBSD rand_r
// implementation.
#define _dispatch_contention_spins() ({ \
static unsigned int _seed; \
((unsigned int)rand_r(&_seed) & (DISPATCH_CONTENTION_SPINS_MAX)) | \
Expand Down Expand Up @@ -141,8 +145,13 @@
#pragma mark _dispatch_contention_usleep

#ifndef DISPATCH_CONTENTION_USLEEP_START
#if defined(_WIN32)
#define DISPATCH_CONTENTION_USLEEP_START 1000 // Must be >= 1ms for Sleep()
#else
#define DISPATCH_CONTENTION_USLEEP_START 500
#endif
#endif

#ifndef DISPATCH_CONTENTION_USLEEP_MAX
#define DISPATCH_CONTENTION_USLEEP_MAX 100000
#endif
Expand All @@ -155,25 +164,10 @@
#define _dispatch_contention_usleep(u) thread_switch(MACH_PORT_NULL, \
SWITCH_OPTION_WAIT, (((u)-1)/1000)+1)
#endif
#else
#if defined(_WIN32)
DISPATCH_INLINE void
_dispatch_contention_usleep(uint64_t useconds) {
static BOOL bQPFExecuted = FALSE;
static LARGE_INTEGER liFreq;
LARGE_INTEGER liStart, liNow;

if (!bQPFExecuted)
bQPFExecuted = QueryPerformanceFrequency(&liFreq);

QueryPerformanceCounter(&liStart);
do {
QueryPerformanceCounter(&liNow);
} while ((liNow.QuadPart - liStart.QuadPart) / (float)liFreq.QuadPart * 1000 * 1000 < useconds);
}
#elif defined(_WIN32)
#define _dispatch_contention_usleep(u) Sleep((u) / 1000)
#else
#define _dispatch_contention_usleep(u) usleep((u))
#endif
#endif // HAVE_MACH

#endif // __DISPATCH_SHIMS_YIELD__