| 1 | // Copyright 2019 The Go Authors. All rights reserved. |
|---|---|
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | package imports |
| 6 | |
| 7 | import ( |
| 8 | "context" |
| 9 | "fmt" |
| 10 | "sync" |
| 11 | |
| 12 | "golang.org/x/tools/internal/gopathwalk" |
| 13 | ) |
| 14 | |
| 15 | // To find packages to import, the resolver needs to know about all of the |
| 16 | // the packages that could be imported. This includes packages that are |
| 17 | // already in modules that are in (1) the current module, (2) replace targets, |
| 18 | // and (3) packages in the module cache. Packages in (1) and (2) may change over |
| 19 | // time, as the client may edit the current module and locally replaced modules. |
| 20 | // The module cache (which includes all of the packages in (3)) can only |
| 21 | // ever be added to. |
| 22 | // |
| 23 | // The resolver can thus save state about packages in the module cache |
| 24 | // and guarantee that this will not change over time. To obtain information |
| 25 | // about new modules added to the module cache, the module cache should be |
| 26 | // rescanned. |
| 27 | // |
| 28 | // It is OK to serve information about modules that have been deleted, |
| 29 | // as they do still exist. |
| 30 | // TODO(suzmue): can we share information with the caller about |
| 31 | // what module needs to be downloaded to import this package? |
| 32 | |
| 33 | type directoryPackageStatus int |
| 34 | |
| 35 | const ( |
| 36 | _ directoryPackageStatus = iota |
| 37 | directoryScanned |
| 38 | nameLoaded |
| 39 | exportsLoaded |
| 40 | ) |
| 41 | |
| 42 | type directoryPackageInfo struct { |
| 43 | // status indicates the extent to which this struct has been filled in. |
| 44 | status directoryPackageStatus |
| 45 | // err is non-nil when there was an error trying to reach status. |
| 46 | err error |
| 47 | |
| 48 | // Set when status >= directoryScanned. |
| 49 | |
| 50 | // dir is the absolute directory of this package. |
| 51 | dir string |
| 52 | rootType gopathwalk.RootType |
| 53 | // nonCanonicalImportPath is the package's expected import path. It may |
| 54 | // not actually be importable at that path. |
| 55 | nonCanonicalImportPath string |
| 56 | |
| 57 | // Module-related information. |
| 58 | moduleDir string // The directory that is the module root of this dir. |
| 59 | moduleName string // The module name that contains this dir. |
| 60 | |
| 61 | // Set when status >= nameLoaded. |
| 62 | |
| 63 | packageName string // the package name, as declared in the source. |
| 64 | |
| 65 | // Set when status >= exportsLoaded. |
| 66 | |
| 67 | exports []string |
| 68 | } |
| 69 | |
| 70 | // reachedStatus returns true when info has a status at least target and any error associated with |
| 71 | // an attempt to reach target. |
| 72 | func (info *directoryPackageInfo) reachedStatus(target directoryPackageStatus) (bool, error) { |
| 73 | if info.err == nil { |
| 74 | return info.status >= target, nil |
| 75 | } |
| 76 | if info.status == target { |
| 77 | return true, info.err |
| 78 | } |
| 79 | return true, nil |
| 80 | } |
| 81 | |
| 82 | // dirInfoCache is a concurrency safe map for storing information about |
| 83 | // directories that may contain packages. |
| 84 | // |
| 85 | // The information in this cache is built incrementally. Entries are initialized in scan. |
| 86 | // No new keys should be added in any other functions, as all directories containing |
| 87 | // packages are identified in scan. |
| 88 | // |
| 89 | // Other functions, including loadExports and findPackage, may update entries in this cache |
| 90 | // as they discover new things about the directory. |
| 91 | // |
| 92 | // The information in the cache is not expected to change for the cache's |
| 93 | // lifetime, so there is no protection against competing writes. Users should |
| 94 | // take care not to hold the cache across changes to the underlying files. |
| 95 | // |
| 96 | // TODO(suzmue): consider other concurrency strategies and data structures (RWLocks, sync.Map, etc) |
| 97 | type dirInfoCache struct { |
| 98 | mu sync.Mutex |
| 99 | // dirs stores information about packages in directories, keyed by absolute path. |
| 100 | dirs map[string]*directoryPackageInfo |
| 101 | listeners map[*int]cacheListener |
| 102 | } |
| 103 | |
| 104 | type cacheListener func(directoryPackageInfo) |
| 105 | |
| 106 | // ScanAndListen calls listener on all the items in the cache, and on anything |
| 107 | // newly added. The returned stop function waits for all in-flight callbacks to |
| 108 | // finish and blocks new ones. |
| 109 | func (d *dirInfoCache) ScanAndListen(ctx context.Context, listener cacheListener) func() { |
| 110 | ctx, cancel := context.WithCancel(ctx) |
| 111 | |
| 112 | // Flushing out all the callbacks is tricky without knowing how many there |
| 113 | // are going to be. Setting an arbitrary limit makes it much easier. |
| 114 | const maxInFlight = 10 |
| 115 | sema := make(chan struct{}, maxInFlight) |
| 116 | for i := 0; i < maxInFlight; i++ { |
| 117 | sema <- struct{}{} |
| 118 | } |
| 119 | |
| 120 | cookie := new(int) // A unique ID we can use for the listener. |
| 121 | |
| 122 | // We can't hold mu while calling the listener. |
| 123 | d.mu.Lock() |
| 124 | var keys []string |
| 125 | for key := range d.dirs { |
| 126 | keys = append(keys, key) |
| 127 | } |
| 128 | d.listeners[cookie] = func(info directoryPackageInfo) { |
| 129 | select { |
| 130 | case <-ctx.Done(): |
| 131 | return |
| 132 | case <-sema: |
| 133 | } |
| 134 | listener(info) |
| 135 | sema <- struct{}{} |
| 136 | } |
| 137 | d.mu.Unlock() |
| 138 | |
| 139 | stop := func() { |
| 140 | cancel() |
| 141 | d.mu.Lock() |
| 142 | delete(d.listeners, cookie) |
| 143 | d.mu.Unlock() |
| 144 | for i := 0; i < maxInFlight; i++ { |
| 145 | <-sema |
| 146 | } |
| 147 | } |
| 148 | |
| 149 | // Process the pre-existing keys. |
| 150 | for _, k := range keys { |
| 151 | select { |
| 152 | case <-ctx.Done(): |
| 153 | return stop |
| 154 | default: |
| 155 | } |
| 156 | if v, ok := d.Load(k); ok { |
| 157 | listener(v) |
| 158 | } |
| 159 | } |
| 160 | |
| 161 | return stop |
| 162 | } |
| 163 | |
| 164 | // Store stores the package info for dir. |
| 165 | func (d *dirInfoCache) Store(dir string, info directoryPackageInfo) { |
| 166 | d.mu.Lock() |
| 167 | _, old := d.dirs[dir] |
| 168 | d.dirs[dir] = &info |
| 169 | var listeners []cacheListener |
| 170 | for _, l := range d.listeners { |
| 171 | listeners = append(listeners, l) |
| 172 | } |
| 173 | d.mu.Unlock() |
| 174 | |
| 175 | if !old { |
| 176 | for _, l := range listeners { |
| 177 | l(info) |
| 178 | } |
| 179 | } |
| 180 | } |
| 181 | |
| 182 | // Load returns a copy of the directoryPackageInfo for absolute directory dir. |
| 183 | func (d *dirInfoCache) Load(dir string) (directoryPackageInfo, bool) { |
| 184 | d.mu.Lock() |
| 185 | defer d.mu.Unlock() |
| 186 | info, ok := d.dirs[dir] |
| 187 | if !ok { |
| 188 | return directoryPackageInfo{}, false |
| 189 | } |
| 190 | return *info, true |
| 191 | } |
| 192 | |
| 193 | // Keys returns the keys currently present in d. |
| 194 | func (d *dirInfoCache) Keys() (keys []string) { |
| 195 | d.mu.Lock() |
| 196 | defer d.mu.Unlock() |
| 197 | for key := range d.dirs { |
| 198 | keys = append(keys, key) |
| 199 | } |
| 200 | return keys |
| 201 | } |
| 202 | |
| 203 | func (d *dirInfoCache) CachePackageName(info directoryPackageInfo) (string, error) { |
| 204 | if loaded, err := info.reachedStatus(nameLoaded); loaded { |
| 205 | return info.packageName, err |
| 206 | } |
| 207 | if scanned, err := info.reachedStatus(directoryScanned); !scanned || err != nil { |
| 208 | return "", fmt.Errorf("cannot read package name, scan error: %v", err) |
| 209 | } |
| 210 | info.packageName, info.err = packageDirToName(info.dir) |
| 211 | info.status = nameLoaded |
| 212 | d.Store(info.dir, info) |
| 213 | return info.packageName, info.err |
| 214 | } |
| 215 | |
| 216 | func (d *dirInfoCache) CacheExports(ctx context.Context, env *ProcessEnv, info directoryPackageInfo) (string, []string, error) { |
| 217 | if reached, _ := info.reachedStatus(exportsLoaded); reached { |
| 218 | return info.packageName, info.exports, info.err |
| 219 | } |
| 220 | if reached, err := info.reachedStatus(nameLoaded); reached && err != nil { |
| 221 | return "", nil, err |
| 222 | } |
| 223 | info.packageName, info.exports, info.err = loadExportsFromFiles(ctx, env, info.dir, false) |
| 224 | if info.err == context.Canceled || info.err == context.DeadlineExceeded { |
| 225 | return info.packageName, info.exports, info.err |
| 226 | } |
| 227 | // The cache structure wants things to proceed linearly. We can skip a |
| 228 | // step here, but only if we succeed. |
| 229 | if info.status == nameLoaded || info.err == nil { |
| 230 | info.status = exportsLoaded |
| 231 | } else { |
| 232 | info.status = nameLoaded |
| 233 | } |
| 234 | d.Store(info.dir, info) |
| 235 | return info.packageName, info.exports, info.err |
| 236 | } |
| 237 |
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