github.com/MerlinKodo/gvisor@v0.0.0-20231110090155-957f62ecf90e/pkg/flipcall/futex_linux.go (about)

     1  // Copyright 2019 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  //go:build linux
    16  // +build linux
    17  
    18  package flipcall
    19  
    20  import (
    21  	"fmt"
    22  	"runtime"
    23  
    24  	"golang.org/x/sys/unix"
    25  	"github.com/MerlinKodo/gvisor/pkg/abi/linux"
    26  )
    27  
    28  func (ep *Endpoint) futexSetPeerActive() error {
    29  	if ep.connState().CompareAndSwap(ep.activeState, ep.inactiveState) {
    30  		return nil
    31  	}
    32  	switch cs := ep.connState().Load(); cs {
    33  	case csShutdown:
    34  		return ShutdownError{}
    35  	default:
    36  		return fmt.Errorf("unexpected connection state before FUTEX_WAKE: %v", cs)
    37  	}
    38  }
    39  
    40  func (ep *Endpoint) futexWakePeer() error {
    41  	if err := ep.futexWakeConnState(1); err != nil {
    42  		return fmt.Errorf("failed to FUTEX_WAKE peer Endpoint: %v", err)
    43  	}
    44  	return nil
    45  }
    46  
    47  func (ep *Endpoint) futexWaitUntilActive() error {
    48  	for {
    49  		switch cs := ep.connState().Load(); cs {
    50  		case ep.activeState:
    51  			return nil
    52  		case ep.inactiveState:
    53  			if ep.isShutdownLocally() {
    54  				return ShutdownError{}
    55  			}
    56  			if err := ep.futexWaitConnState(ep.inactiveState); err != nil {
    57  				return fmt.Errorf("failed to FUTEX_WAIT for peer Endpoint: %v", err)
    58  			}
    59  			continue
    60  		case csShutdown:
    61  			return ShutdownError{}
    62  		default:
    63  			return fmt.Errorf("unexpected connection state before FUTEX_WAIT: %v", cs)
    64  		}
    65  	}
    66  }
    67  
    68  func (ep *Endpoint) futexWakeConnState(numThreads int32) error {
    69  	if _, _, e := unix.RawSyscall(unix.SYS_FUTEX, ep.packet, linux.FUTEX_WAKE, uintptr(numThreads)); e != 0 {
    70  		return e
    71  	}
    72  	return nil
    73  }
    74  
    75  func (ep *Endpoint) futexWaitConnState(curState uint32) error {
    76  	_, _, e := unix.Syscall6(unix.SYS_FUTEX, ep.packet, linux.FUTEX_WAIT, uintptr(curState), 0, 0, 0)
    77  	if e != 0 && e != unix.EAGAIN && e != unix.EINTR {
    78  		return e
    79  	}
    80  	return nil
    81  }
    82  
    83  func yieldThread() {
    84  	unix.Syscall(unix.SYS_SCHED_YIELD, 0, 0, 0)
    85  	// The thread we're trying to yield to may be waiting for a Go runtime P.
    86  	// runtime.Gosched() will hand off ours if necessary.
    87  	runtime.Gosched()
    88  }