golang time_fake 代码
文件路径：/src/runtime/time_fake.go
/ Copyright 2019 The Go Authors. All rights reserved.
/ Use of this source code is governed by a BSD-style
/ license that can be found in the LICENSE file.
/go:build faketime && !windows
/ Faketime isn't currently supported on Windows. This would require
/ modifying syscall.Write to call syscall.faketimeWrite,
/ translating the Stdout and Stderr handles into FDs 1 and 2.
/ (See CL 192739 PS 3.)
package runtime
import "unsafe"
/ faketime is the simulated time in nanoseconds since 1970 for the
/ playground.
var faketime int64 = 1257894000000000000
var faketimeState struct {
lock mutex
/ lastfaketime is the last faketime value written to fd 1 or 2.
lastfaketime int64
/ lastfd is the fd to which lastfaketime was written.
/
/ Subsequent writes to the same fd may use the same
/ timestamp, but the timestamp must increase if the fd
/ changes.
lastfd uintptr
}
/go:nosplit
func nanotime() int64 {
return faketime
}
/go:linkname time_now time.now
func time_now() (sec int64, nsec int32, mono int64) {
return faketime / 1e9, int32(faketime % 1e9), faketime
}
/ write is like the Unix write system call.
/ We have to avoid write barriers to avoid potential deadlock
/ on write calls.
/
/go:nowritebarrierrec
func write(fd uintptr, p unsafe.Pointer, n int32) int32 {
if !(fd == 1 || fd == 2) {
/ Do an ordinary write.
return write1(fd, p, n)
}
/ Write with the playback header.
/ First, lock to avoid interleaving writes.
lock(&faketimeState.lock)
/ If the current fd doesn't match the fd of the previous write,
/ ensure that the timestamp is strictly greater. That way, we can
/ recover the original order even if we read the fds separately.
t := faketimeState.lastfaketime
if fd != faketimeState.lastfd {
t++
faketimeState.lastfd = fd
}
if faketime > t {
t = faketime
}
faketimeState.lastfaketime = t
/ Playback header: 0 0 P B <8-byte time> <4-byte data length> (big endian)
var buf [4 + 8 + 4]byte
buf[2] = 'P'
buf[3] = 'B'
tu := uint64(t)
buf[4] = byte(tu >> (7 * 8))
buf[5] = byte(tu >> (6 * 8))
buf[6] = byte(tu >> (5 * 8))
buf[7] = byte(tu >> (4 * 8))
buf[8] = byte(tu >> (3 * 8))
buf[9] = byte(tu >> (2 * 8))
buf[10] = byte(tu >> (1 * 8))
buf[11] = byte(tu >> (0 * 8))
nu := uint32(n)
buf[12] = byte(nu >> (3 * 8))
buf[13] = byte(nu >> (2 * 8))
buf[14] = byte(nu >> (1 * 8))
buf[15] = byte(nu >> (0 * 8))
write1(fd, unsafe.Pointer(&buf[0]), int32(len(buf)))
/ Write actual data.
res := write1(fd, p, n)
unlock(&faketimeState.lock)
return res
}