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/*-
* Copyright (c) 2014-2020 MongoDB, Inc.
* Copyright (c) 2008-2014 WiredTiger, Inc.
* All rights reserved.
*
* See the file LICENSE for redistribution information.
*/
#include "wt_internal.h"
WT_PROCESS __wt_process; /* Per-process structure */
static int __wt_pthread_once_failed; /* If initialization failed */
/*
* __endian_check --
* Check the build matches the machine.
*/
static int
__endian_check(void)
{
uint64_t v;
const char *e;
bool big;
v = 1;
big = *((uint8_t *)&v) == 0;
#ifdef WORDS_BIGENDIAN
if (big)
return (0);
e = "big-endian";
#else
if (!big)
return (0);
e = "little-endian";
#endif
fprintf(stderr,
"This is a %s build of the WiredTiger data engine, incompatible "
"with this system\n",
e);
return (EINVAL);
}
/*
* __global_calibrate_ticks --
* Calibrate a ratio from rdtsc ticks to nanoseconds.
*/
static void
__global_calibrate_ticks(void)
{
/*
* Default to using __wt_epoch until we have a good value for the ratio.
*/
__wt_process.tsc_nsec_ratio = WT_TSC_DEFAULT_RATIO;
__wt_process.use_epochtime = true;
#if defined(__i386) || defined(__amd64)
{
struct timespec start, stop;
double ratio;
uint64_t diff_nsec, diff_tsc, min_nsec, min_tsc;
uint64_t tries, tsc_start, tsc_stop;
volatile uint64_t i;
/*
* Run this calibration loop a few times to make sure we get a reading that does not have a
* potential scheduling shift in it. The inner loop is CPU intensive but a scheduling change
* in the middle could throw off calculations. Take the minimum amount of time and compute
* the ratio.
*/
min_nsec = min_tsc = UINT64_MAX;
for (tries = 0; tries < 3; ++tries) {
/* This needs to be CPU intensive and large enough. */
__wt_epoch(NULL, &start);
tsc_start = __wt_rdtsc();
for (i = 0; i < 100 * WT_MILLION; i++)
;
tsc_stop = __wt_rdtsc();
__wt_epoch(NULL, &stop);
diff_nsec = WT_TIMEDIFF_NS(stop, start);
diff_tsc = tsc_stop - tsc_start;
/* If the clock didn't tick over, we don't have a sample. */
if (diff_nsec == 0 || diff_tsc == 0)
continue;
min_nsec = WT_MIN(min_nsec, diff_nsec);
min_tsc = WT_MIN(min_tsc, diff_tsc);
}
/*
* Only use rdtsc if we got a good reading. One reason this might fail is that the system's
* clock granularity is not fine-grained enough.
*/
if (min_nsec != UINT64_MAX) {
ratio = (double)min_tsc / (double)min_nsec;
if (ratio > DBL_EPSILON) {
__wt_process.tsc_nsec_ratio = ratio;
__wt_process.use_epochtime = false;
}
}
}
#endif
}
/*
* __global_once --
* Global initialization, run once.
*/
static void
__global_once(void)
{
WT_DECL_RET;
if ((ret = __wt_spin_init(NULL, &__wt_process.spinlock, "global")) != 0) {
__wt_pthread_once_failed = ret;
return;
}
TAILQ_INIT(&__wt_process.connqh);
/*
* Set up the checksum functions. If there's only one, set it as the alternate, that way code
* doesn't have to check if it's set or not.
*/
__wt_process.checksum = wiredtiger_crc32c_func();
__global_calibrate_ticks();
}
/*
* __wt_library_init --
* Some things to do, before we do anything else.
*/
int
__wt_library_init(void)
{
static bool first = true;
WT_DECL_RET;
/* Check the build matches the machine. */
WT_RET(__endian_check());
/*
* Do per-process initialization once, before anything else, but only once. I don't know how
* heavy-weight the function (pthread_once, in the POSIX world), might be, so I'm front-ending
* it with a local static and only using that function to avoid a race.
*/
if (first) {
if ((ret = __wt_once(__global_once)) != 0)
__wt_pthread_once_failed = ret;
first = false;
}
return (__wt_pthread_once_failed);
}
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