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-rw-r--r--src/runtime/time_fake.go98
1 files changed, 98 insertions, 0 deletions
diff --git a/src/runtime/time_fake.go b/src/runtime/time_fake.go
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+// 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
+}