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| 1 | +//go:build js || wasip1 |
| 2 | +// +build js wasip1 |
| 3 | + |
| 4 | +/* |
| 5 | + * Copyright 2017 Dgraph Labs, Inc. and Contributors |
| 6 | + * |
| 7 | + * Licensed under the Apache License, Version 2.0 (the "License"); |
| 8 | + * you may not use this file except in compliance with the License. |
| 9 | + * You may obtain a copy of the License at |
| 10 | + * |
| 11 | + * http://www.apache.org/licenses/LICENSE-2.0 |
| 12 | + * |
| 13 | + * Unless required by applicable law or agreed to in writing, software |
| 14 | + * distributed under the License is distributed on an "AS IS" BASIS, |
| 15 | + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 16 | + * See the License for the specific language governing permissions and |
| 17 | + * limitations under the License. |
| 18 | + */ |
| 19 | + |
| 20 | +package badger |
| 21 | + |
| 22 | +import ( |
| 23 | + "fmt" |
| 24 | + "os" |
| 25 | + "path/filepath" |
| 26 | + |
| 27 | + "github.com/dgraph-io/badger/v4/y" |
| 28 | +) |
| 29 | + |
| 30 | +// directoryLockGuard holds a lock on a directory and a pid file inside. The pid file isn't part |
| 31 | +// of the locking mechanism, it's just advisory. |
| 32 | +type directoryLockGuard struct { |
| 33 | + // File handle on the directory, which we've flocked. |
| 34 | + f *os.File |
| 35 | + // The absolute path to our pid file. |
| 36 | + path string |
| 37 | + // Was this a shared lock for a read-only database? |
| 38 | + readOnly bool |
| 39 | +} |
| 40 | + |
| 41 | +// acquireDirectoryLock gets a lock on the directory (using flock). If |
| 42 | +// this is not read-only, it will also write our pid to |
| 43 | +// dirPath/pidFileName for convenience. |
| 44 | +func acquireDirectoryLock(dirPath string, pidFileName string, readOnly bool) ( |
| 45 | + *directoryLockGuard, error) { |
| 46 | + // Convert to absolute path so that Release still works even if we do an unbalanced |
| 47 | + // chdir in the meantime. |
| 48 | + absPidFilePath, err := filepath.Abs(filepath.Join(dirPath, pidFileName)) |
| 49 | + if err != nil { |
| 50 | + return nil, y.Wrapf(err, "cannot get absolute path for pid lock file") |
| 51 | + } |
| 52 | + f, err := os.Open(dirPath) |
| 53 | + if err != nil { |
| 54 | + return nil, y.Wrapf(err, "cannot open directory %q", dirPath) |
| 55 | + } |
| 56 | + |
| 57 | + // NOTE: Here is where we would normally call flock. |
| 58 | + // This is not supported in js / wasm, so skip it. |
| 59 | + |
| 60 | + if !readOnly { |
| 61 | + // Yes, we happily overwrite a pre-existing pid file. We're the |
| 62 | + // only read-write badger process using this directory. |
| 63 | + err = os.WriteFile(absPidFilePath, []byte(fmt.Sprintf("%d\n", os.Getpid())), 0666) |
| 64 | + if err != nil { |
| 65 | + f.Close() |
| 66 | + return nil, y.Wrapf(err, |
| 67 | + "Cannot write pid file %q", absPidFilePath) |
| 68 | + } |
| 69 | + } |
| 70 | + |
| 71 | + return &directoryLockGuard{f, absPidFilePath, readOnly}, nil |
| 72 | +} |
| 73 | + |
| 74 | +// Release deletes the pid file and releases our lock on the directory. |
| 75 | +func (guard *directoryLockGuard) release() error { |
| 76 | + var err error |
| 77 | + if !guard.readOnly { |
| 78 | + // It's important that we remove the pid file first. |
| 79 | + err = os.Remove(guard.path) |
| 80 | + } |
| 81 | + |
| 82 | + if closeErr := guard.f.Close(); err == nil { |
| 83 | + err = closeErr |
| 84 | + } |
| 85 | + guard.path = "" |
| 86 | + guard.f = nil |
| 87 | + |
| 88 | + return err |
| 89 | +} |
| 90 | + |
| 91 | +// openDir opens a directory for syncing. |
| 92 | +func openDir(path string) (*os.File, error) { return os.Open(path) } |
| 93 | + |
| 94 | +// When you create or delete a file, you have to ensure the directory entry for the file is synced |
| 95 | +// in order to guarantee the file is visible (if the system crashes). (See the man page for fsync, |
| 96 | +// or see https://github.com/coreos/etcd/issues/6368 for an example.) |
| 97 | +func syncDir(dir string) error { |
| 98 | + f, err := openDir(dir) |
| 99 | + if err != nil { |
| 100 | + return y.Wrapf(err, "While opening directory: %s.", dir) |
| 101 | + } |
| 102 | + |
| 103 | + err = f.Sync() |
| 104 | + closeErr := f.Close() |
| 105 | + if err != nil { |
| 106 | + return y.Wrapf(err, "While syncing directory: %s.", dir) |
| 107 | + } |
| 108 | + return y.Wrapf(closeErr, "While closing directory: %s.", dir) |
| 109 | +} |
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