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Assure accurate elapsedRealTimeNanos calculations

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If a context switch or interrupt happens between
getting current time and getting boot time, this
can throw off the calculation for the
elapsedRealTimeNanos timestamp. Avoid this by
retrying if there is a large enough delta
between getting current time and getting boot
time.

Change-Id: I47d7a99b480423a50eaf951a904f21928587eda6
CRs-fixed: 2541719
This commit is contained in:
Dante Russo 2019-09-30 16:24:03 -07:00
parent 2379d8bc30
commit f80980210e
1 changed files with 37 additions and 4 deletions
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41
android/2.0/location_api/LocationUtil.cpp
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@ -88,10 +88,41 @@ void convertGnssLocation(Location& in, V2_0::GnssLocation& out)
struct timespec sinceBootTime;
struct timespec currentTime;
if (0 == clock_gettime(CLOCK_BOOTTIME,&sinceBootTime) &&
0 == clock_gettime(CLOCK_REALTIME,&currentTime)) {
struct timespec sinceBootTimeTest;
int64_t sinceBootTimeNanos = 0;
bool clockGetTimeSuccess = false;
const uint32_t MAX_TIME_DELTA_VALUE_NANOS = 10000;
const uint32_t MAX_GET_TIME_COUNT = 20;
/* Attempt to get CLOCK_REALTIME and CLOCK_BOOTIME in succession without an interruption
or context switch (for up to MAX_GET_TIME_COUNT times) to avoid errors in the calculation */
for (uint32_t i=0; i < MAX_GET_TIME_COUNT; i++) {
if (clock_gettime(CLOCK_BOOTTIME, &sinceBootTime) != 0) {
break;
};
if (clock_gettime(CLOCK_REALTIME, &currentTime) != 0) {
break;
}
if (clock_gettime(CLOCK_BOOTTIME, &sinceBootTimeTest) != 0) {
break;
};
sinceBootTimeNanos = sinceBootTime.tv_sec*1000000000 + sinceBootTime.tv_nsec;
int64_t sinceBootTimeTestNanos =
sinceBootTimeTest.tv_sec*1000000000 + sinceBootTimeTest.tv_nsec;
int64_t sinceBootTimeDeltaNanos = sinceBootTimeTestNanos - sinceBootTimeNanos;
int64_t sinceBootTimeNanos = sinceBootTime.tv_sec*1000000000 + sinceBootTime.tv_nsec;
/* sinceBootTime and sinceBootTimeTest should have a close value if there was no
interruption or context switch between clock_gettime for CLOCK_BOOTIME and
clock_gettime for CLOCK_REALTIME */
if (sinceBootTimeDeltaNanos < MAX_TIME_DELTA_VALUE_NANOS) {
clockGetTimeSuccess = true;
break;
} else {
LOC_LOGD("%s]: Delta:%" PRIi64 "ns time too large, retry number #%u...",
__FUNCTION__, sinceBootTimeDeltaNanos, i+1);
}
}
if (clockGetTimeSuccess) {
int64_t currentTimeNanos = currentTime.tv_sec*1000000000 + currentTime.tv_nsec;
int64_t locationTimeNanos = in.timestamp*1000000;
LOC_LOGD("%s]: sinceBootTimeNanos:%" PRIi64 " currentTimeNanos:%" PRIi64 ""
@ -110,8 +141,10 @@ void convertGnssLocation(Location& in, V2_0::GnssLocation& out)
__FUNCTION__, out.elapsedRealtime.timestampNs);
}
}
} else {
LOC_LOGE("%s]: Failed to calculate elapsedRealtimeNanos timestamp after %u tries",
__FUNCTION__, MAX_GET_TIME_COUNT);
}
}
void convertGnssLocation(const V1_0::GnssLocation& in, Location& out)