67e26be2d9
The public tree and its history contain only the listed paths. Earlier projection history remains preserved internally. Source-Sha: 913fde029b935671833254797f0f20f1eb9fabba Policy-Sha: 913fde029b935671833254797f0f20f1eb9fabba Tree-Digest: 180ae530c1058a2a5c89837bdce2d323ae83e669e38590ca72e75b8d92b7262f
45 lines
1.2 KiB
Go
45 lines
1.2 KiB
Go
//go:build linux || darwin || freebsd
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package instancelock
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import (
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"fmt"
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"os"
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"path/filepath"
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"syscall"
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)
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// acquireLock opens (or creates) the lockfile and takes an exclusive
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// flock. The lock is released when the process exits (the kernel
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// closes the fd, which releases the flock).
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func acquireLock() (func(), error) {
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path := LockPath()
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dir := filepath.Dir(path)
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if err := os.MkdirAll(dir, 0755); err != nil {
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return nil, fmt.Errorf("instancelock: mkdir %s: %w", dir, err)
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}
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f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0644)
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if err != nil {
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return nil, fmt.Errorf("instancelock: open %s: %w", path, err)
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}
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fd := int(f.Fd())
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if err := syscall.Flock(fd, syscall.LOCK_EX|syscall.LOCK_NB); err != nil {
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f.Close()
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return nil, fmt.Errorf("instancelock: %s is locked by another process: %w", path, err)
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}
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// Write our PID so operators can see who holds the lock.
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_, _ = f.WriteAt([]byte(fmt.Sprintf("%d\n", os.Getpid())), 0)
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_ = f.Truncate(64)
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release := func() {
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_ = f.Close()
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// Don't remove the file — leaving it is harmless and prevents a
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// TOCTOU race where a fresh open might get an unlocked fd before
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// we flock it.
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}
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return release, nil
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}
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