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/**
* @file llcond.cpp
* @author Nat Goodspeed
* @date 2019-07-17
* @brief Implementation for llcond.
*
* $LicenseInfo:firstyear=2019&license=viewerlgpl$
* Copyright (c) 2019, Linden Research, Inc.
* $/LicenseInfo$
*/
// Precompiled header
#include "linden_common.h"
// associated header
#include "llcond.h"
// STL headers
// std headers
// external library headers
// other Linden headers
namespace // anonymous
{
// See comments in LLCond::convert(const LLDate&) below
std::time_t compute_lldate_epoch()
{
LLDate lldate_epoch;
std::tm tm;
// It should be noted that calling LLDate::split() to write directly
// into a std::tm struct depends on S32 being a typedef for int in
// stdtypes.h: split() takes S32*, whereas tm fields are documented to
// be int. If you get compile errors here, somebody changed the
// definition of S32. You'll have to declare six S32 variables,
// split() into them, then assign them into the relevant tm fields.
if (! lldate_epoch.split(&tm.tm_year, &tm.tm_mon, &tm.tm_mday,
&tm.tm_hour, &tm.tm_min, &tm.tm_sec))
{
// Theoretically split() could return false. In that case, we
// don't have valid data, so we can't compute offset, so skip the
// rest of this.
return 0;
}
tm.tm_isdst = 0;
std::time_t lldate_epoch_time = std::mktime(&tm);
if (lldate_epoch_time == -1)
{
// Theoretically mktime() could return -1, meaning that the contents
// of the passed std::tm cannot be represented as a time_t. (Worrisome
// if LLDate's epoch happened to be exactly 1 tick before
// std::time_t's epoch...)
// In the error case, assume offset 0.
return 0;
}
// But if we got this far, lldate_epoch_time is the time_t we want.
return lldate_epoch_time;
}
} // anonymous namespace
// convert LLDate to a chrono::time_point
std::chrono::system_clock::time_point LLCond::convert(const LLDate& lldate)
{
// std::chrono::system_clock's epoch MAY be the Unix epoch, namely
// midnight UTC on 1970-01-01, in fact it probably is. But until C++20,
// system_clock does not guarantee that. Unfortunately time_t doesn't
// specify its epoch either, other than to note that it "almost always" is
// the Unix epoch (https://en.cppreference.com/w/cpp/chrono/c/time_t).
// LLDate, being based on apr_time_t, does guarantee 1970-01-01T00:00 UTC.
// http://apr.apache.org/docs/apr/1.5/group__apr__time.html#gadb4bde16055748190eae190c55aa02bb
// The easy, efficient conversion would be
// std::chrono::system_clock::from_time_t(std::time_t(LLDate::secondsSinceEpoch())).
// But that assumes that both time_t and system_clock have the same epoch
// as LLDate -- an assumption that will work until it unexpectedly doesn't.
// It would be more formally correct to break out the year, month, day,
// hour, minute, second (UTC) using LLDate::split() and recombine them
// into std::time_t using std::mktime(). However, both split() and
// mktime() have integer second granularity, whereas callers of
// wait_until() are very likely to be interested in sub-second precision.
// In that sense std::chrono::system_clock::from_time_t() is still
// preferred.
// So use the split() / mktime() mechanism to determine the numeric value
// of the LLDate / apr_time_t epoch as expressed in time_t. (We assume
// that the epoch offset can be expressed as integer seconds, per split()
// and mktime(), which seems plausible.)
// n.b. A function-static variable is initialized only once in a
// thread-safe way.
static std::time_t lldate_epoch_time = compute_lldate_epoch();
// LLDate::secondsSinceEpoch() gets us, of course, how long it has
// been since lldate_epoch_time. So adding lldate_epoch_time should
// give us the correct time_t representation of a given LLDate even if
// time_t's epoch differs from LLDate's.
// We don't have to worry about the relative epochs of time_t and
// system_clock because from_time_t() takes care of that!
return std::chrono::system_clock::from_time_t(lldate_epoch_time +
lldate.secondsSinceEpoch());
}
// convert F32Milliseconds to a chrono::duration
std::chrono::milliseconds LLCond::convert(F32Milliseconds)
{
// extract the F32 milliseconds from F32Milliseconds, construct
// std::chrono::milliseconds from that value
return std::chrono::milliseconds(timeout_duration.value());
}
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