library: os, syscall

internal/lib/os/wait_wait6.go

@@ -0,0 +1,32 @@
+// Copyright 2016 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 dragonfly || freebsd || netbsd
+
+package os
+
+import (
+	"syscall"
+)
+
+// blockUntilWaitable attempts to block until a call to p.Wait will
+// succeed immediately, and reports whether it has done so.
+// It does not actually call p.Wait.
+func (p *Process) blockUntilWaitable() (bool, error) {
+	var errno syscall.Errno
+	for {
+		_, errno = wait6(_P_PID, p.Pid, syscall.WEXITED|syscall.WNOWAIT)
+		if errno != syscall.EINTR {
+			break
+		}
+	}
+	// TODO(xsw):
+	// runtime.KeepAlive(p)
+	if errno == syscall.ENOSYS {
+		return false, nil
+	} else if errno != 0 {
+		return false, NewSyscallError("wait6", errno)
+	}
+	return true, nil
+}

internal/lib/os/wait_waitid.go

@@ -0,0 +1,55 @@
+// Copyright 2016 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.
+
+// We used to used this code for Darwin, but according to issue #19314
+// waitid returns if the process is stopped, even when using WEXITED.
+
+//go:build linux
+
+package os
+
+import (
+	_ "unsafe"
+
+	"github.com/goplus/llgo/c"
+	"github.com/goplus/llgo/c/syscall"
+)
+
+const _P_PID = 1
+
+// int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);
+//
+//go:linkname waitid C.waitid
+func waitid(idtype, id uintptr, infop *[16]uint64, options c.Int) c.Int
+
+// blockUntilWaitable attempts to block until a call to p.Wait will
+// succeed immediately, and reports whether it has done so.
+// It does not actually call p.Wait.
+func (p *Process) blockUntilWaitable() (bool, error) {
+	// The waitid system call expects a pointer to a siginfo_t,
+	// which is 128 bytes on all Linux systems.
+	// On darwin/amd64, it requires 104 bytes.
+	// We don't care about the values it returns.
+	var siginfo [16]uint64
+	psig := &siginfo[0]
+	var e syscall.Errno
+	for {
+		e = syscall.Errno(waitid(_P_PID, uintptr(p.Pid), psig, syscall.WEXITED|syscall.WNOWAIT, 0, 0))
+		if e != syscall.EINTR {
+			break
+		}
+	}
+	// TODO(xsw):
+	// runtime.KeepAlive(p)
+	if e != 0 {
+		// waitid has been available since Linux 2.6.9, but
+		// reportedly is not available in Ubuntu on Windows.
+		// See issue 16610.
+		if e == syscall.ENOSYS {
+			return false, nil
+		}
+		return false, NewSyscallError("waitid", e)
+	}
+	return true, nil
+}

internal/lib/syscall/forkpipe2.go

@@ -0,0 +1,101 @@
+// Copyright 2017 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 dragonfly || freebsd || linux || netbsd || openbsd || solaris
+
+package syscall
+
+import "sync"
+
+// forkExecPipe atomically opens a pipe with O_CLOEXEC set on both file
+// descriptors.
+func forkExecPipe(p []int) error {
+	return Pipe2(p, O_CLOEXEC)
+}
+
+var (
+	// Guard the forking variable.
+	forkingLock sync.Mutex
+	// Number of goroutines currently forking, and thus the
+	// number of goroutines holding a conceptual write lock
+	// on ForkLock.
+	forking int
+)
+
+// TODO(xsw):
+// hasWaitingReaders reports whether any goroutine is waiting
+// to acquire a read lock on rw. It is defined in the sync package.
+func hasWaitingReaders(rw *sync.RWMutex) bool {
+	panic("todo: syscall.hasWaitingReaders in sync package")
+}
+
+// acquireForkLock acquires a write lock on ForkLock.
+// ForkLock is exported and we've promised that during a fork
+// we will call ForkLock.Lock, so that no other threads create
+// new fds that are not yet close-on-exec before we fork.
+// But that forces all fork calls to be serialized, which is bad.
+// But we haven't promised that serialization, and it is essentially
+// undetectable by other users of ForkLock, which is good.
+// Avoid the serialization by ensuring that ForkLock is locked
+// at the first fork and unlocked when there are no more forks.
+func acquireForkLock() {
+	forkingLock.Lock()
+	defer forkingLock.Unlock()
+
+	if forking == 0 {
+		// There is no current write lock on ForkLock.
+		ForkLock.Lock()
+		forking++
+		return
+	}
+
+	// ForkLock is currently locked for writing.
+
+	if hasWaitingReaders(&ForkLock) {
+		// ForkLock is locked for writing, and at least one
+		// goroutine is waiting to read from it.
+		// To avoid lock starvation, allow readers to proceed.
+		// The simple way to do this is for us to acquire a
+		// read lock. That will block us until all current
+		// conceptual write locks are released.
+		//
+		// Note that this case is unusual on modern systems
+		// with O_CLOEXEC and SOCK_CLOEXEC. On those systems
+		// the standard library should never take a read
+		// lock on ForkLock.
+
+		forkingLock.Unlock()
+
+		ForkLock.RLock()
+		ForkLock.RUnlock()
+
+		forkingLock.Lock()
+
+		// Readers got a chance, so now take the write lock.
+
+		if forking == 0 {
+			ForkLock.Lock()
+		}
+	}
+
+	forking++
+}
+
+// releaseForkLock releases the conceptual write lock on ForkLock
+// acquired by acquireForkLock.
+func releaseForkLock() {
+	forkingLock.Lock()
+	defer forkingLock.Unlock()
+
+	if forking <= 0 {
+		panic("syscall.releaseForkLock: negative count")
+	}
+
+	forking--
+
+	if forking == 0 {
+		// No more conceptual write locks.
+		ForkLock.Unlock()
+	}
+}

internal/lib/syscall/syscall_linux.go

@@ -11,6 +11,65 @@
 
 package syscall
 
+type WaitStatus uint32
+
+// Wait status is 7 bits at bottom, either 0 (exited),
+// 0x7F (stopped), or a signal number that caused an exit.
+// The 0x80 bit is whether there was a core dump.
+// An extra number (exit code, signal causing a stop)
+// is in the high bits. At least that's the idea.
+// There are various irregularities. For example, the
+// "continued" status is 0xFFFF, distinguishing itself
+// from stopped via the core dump bit.
+
+const (
+	mask    = 0x7F
+	core    = 0x80
+	exited  = 0x00
+	stopped = 0x7F
+	shift   = 8
+)
+
+func (w WaitStatus) Exited() bool { return w&mask == exited }
+
+func (w WaitStatus) Signaled() bool { return w&mask != stopped && w&mask != exited }
+
+func (w WaitStatus) Stopped() bool { return w&0xFF == stopped }
+
+func (w WaitStatus) Continued() bool { return w == 0xFFFF }
+
+func (w WaitStatus) CoreDump() bool { return w.Signaled() && w&core != 0 }
+
+func (w WaitStatus) ExitStatus() int {
+	if !w.Exited() {
+		return -1
+	}
+	return int(w>>shift) & 0xFF
+}
+
+func (w WaitStatus) Signal() Signal {
+	if !w.Signaled() {
+		return -1
+	}
+	return Signal(w & mask)
+}
+
+func (w WaitStatus) StopSignal() Signal {
+	if !w.Stopped() {
+		return -1
+	}
+	return Signal(w>>shift) & 0xFF
+}
+
+/* TODO(xsw):
+func (w WaitStatus) TrapCause() int {
+	if w.StopSignal() != SIGTRAP {
+		return -1
+	}
+	return int(w>>shift) >> 8
+}
+*/
+
 func Faccessat(dirfd int, path string, mode uint32, flags int) (err error) {
 	panic("todo: syscall.Faccessat")
 }