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package main
import (
"fmt"
"runtime"
"syscall"
"time"
"unsafe"
"golang.org/x/sys/unix"
)
const sleepSyscallsEmitFor = 2 * time.Second
func sleepSyscalls() error {
deadline := time.Now().Add(sleepSyscallsEmitFor)
for time.Now().Before(deadline) {
if err := syscall.Nanosleep(&syscall.Timespec{Sec: 0, Nsec: 2_000_000}, nil); err != nil && err != syscall.EINTR {
return fmt.Errorf("nanosleep: %w", err)
}
if err := callClockNanosleep(3_000_000); err != nil {
return err
}
// Also exercise the TIMER_ABSTIME (absolute) path so the tracer's
// absolute-sleep handling is covered: the request timespec here is an
// absolute CLOCK_MONOTONIC wakeup time, not a relative duration, so the
// tracer must NOT report it as a sleep duration (see task a20).
if err := callClockNanosleepAbs(2_000_000); err != nil {
return err
}
}
return nil
}
// callClockNanosleep issues a relative clock_nanosleep (flags = 0), sleeping for
// requestedNs nanoseconds.
func callClockNanosleep(requestedNs int64) error {
req := unix.Timespec{Sec: requestedNs / 1_000_000_000, Nsec: requestedNs % 1_000_000_000}
return invokeClockNanosleep(0, &req)
}
// callClockNanosleepAbs issues an absolute clock_nanosleep (flags =
// TIMER_ABSTIME). The request timespec is an absolute CLOCK_MONOTONIC wakeup
// time computed as "now + aheadNs", so the call blocks for roughly aheadNs but
// the request value itself is a multi-decade absolute timestamp, not a
// duration.
func callClockNanosleepAbs(aheadNs int64) error {
var now unix.Timespec
if err := unix.ClockGettime(unix.CLOCK_MONOTONIC, &now); err != nil {
return fmt.Errorf("clock_gettime: %w", err)
}
target := now.Nano() + aheadNs
req := unix.Timespec{Sec: target / 1_000_000_000, Nsec: target % 1_000_000_000}
return invokeClockNanosleep(unix.TIMER_ABSTIME, &req)
}
// invokeClockNanosleep is the shared raw clock_nanosleep syscall wrapper used by
// both the relative and absolute callers.
func invokeClockNanosleep(flags uintptr, req *unix.Timespec) error {
_, _, errno := syscall.RawSyscall6(
unix.SYS_CLOCK_NANOSLEEP,
uintptr(unix.CLOCK_MONOTONIC),
flags,
uintptr(unsafe.Pointer(req)),
0,
0,
0,
)
runtime.KeepAlive(req)
if errno != 0 && errno != syscall.EINTR {
return fmt.Errorf("clock_nanosleep: %w", errno)
}
return nil
}
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