mirror of
https://github.com/opentffoundation/opentf.git
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1d38fd69d8
Signed-off-by: Christian Mesh <christianmesh1@gmail.com> Signed-off-by: Martin Atkins <mart@degeneration.co.uk> Co-authored-by: Martin Atkins <mart@degeneration.co.uk>
102 lines
2.7 KiB
Go
102 lines
2.7 KiB
Go
// Copyright (c) The OpenTofu Authors
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// SPDX-License-Identifier: MPL-2.0
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// Copyright (c) 2023 HashiCorp, Inc.
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// SPDX-License-Identifier: MPL-2.0
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//go:build !windows
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// +build !windows
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package flock
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import (
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"context"
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"fmt"
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"io"
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"os"
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"syscall"
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)
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// use fcntl POSIX locks for the most consistent behavior across platforms, and
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// hopefully some compatibility over NFS and CIFS.
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func Lock(f *os.File) error {
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flock := &syscall.Flock_t{
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Type: syscall.F_RDLCK | syscall.F_WRLCK,
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Whence: int16(io.SeekStart),
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Start: 0,
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Len: 0,
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}
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return syscall.FcntlFlock(f.Fd(), syscall.F_SETLK, flock)
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}
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// LockBlocking is like Lock except that if the lock is currently contended
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// then it blocks until it becomes available.
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//
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// If the given context is cancelled then it returns early with the cancellation
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// error.
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func LockBlocking(ctx context.Context, f *os.File) error {
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flock := &syscall.Flock_t{
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Type: syscall.F_RDLCK | syscall.F_WRLCK,
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Whence: int16(io.SeekStart),
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Start: 0,
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Len: 0,
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}
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ctx, cancel := context.WithCancel(ctx)
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defer cancel()
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c := make(chan error)
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go func() {
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for {
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err := syscall.FcntlFlock(f.Fd(), syscall.F_SETLKW, flock)
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if err == syscall.EINTR {
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// We'll get here if our process gets any signal at all, but
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// not all signals represent cancellation.
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if ctxErr := ctx.Err(); ctxErr != nil {
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err = ctxErr // return the cancellation error instead of generic EINTR
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} else {
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continue // not cancelled yet
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}
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}
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c <- err
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close(c)
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return
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}
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}()
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for {
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select {
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case err := <-c:
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return err
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case <-ctx.Done():
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// We will get here if the cancellation is caused by anything other
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// than a Unix signal, in which case we'll send a signal ourselves
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// to force the waiting goroutine to exit.
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// We use SIGUSR1 here on the assumption that nothing else in
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// OpenTofu uses it. We're sending this to the current pid
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// explicitly because we might have other processes, such as
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// plugins, also running in our process group (which is what we'd
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// signal if using pid 0 here).
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err := syscall.Kill(syscall.Getpid(), syscall.SIGUSR1)
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if err != nil {
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// This should not fail, but if it does then we'd otherwise
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// get hung up here and so we'll return an error and accept
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// that our background goroutine is going to just hang around
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// until another signal shows up or the program exits.
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return fmt.Errorf("failed canceling lock acquisition: %w", err)
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}
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}
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}
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}
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func Unlock(f *os.File) error {
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flock := &syscall.Flock_t{
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Type: syscall.F_UNLCK,
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Whence: int16(io.SeekStart),
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Start: 0,
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Len: 0,
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}
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return syscall.FcntlFlock(f.Fd(), syscall.F_SETLK, flock)
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}
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