diff options
Diffstat (limited to 'src/os/exec/exec.go')
| -rw-r--r-- | src/os/exec/exec.go | 65 |
1 files changed, 35 insertions, 30 deletions
diff --git a/src/os/exec/exec.go b/src/os/exec/exec.go index 50ed3a8d16..da9f68fe28 100644 --- a/src/os/exec/exec.go +++ b/src/os/exec/exec.go @@ -334,8 +334,10 @@ type Cmd struct { lookPathErr error // cachedLookExtensions caches the result of calling lookExtensions. + // It is set when Command is called with an absolute path, letting it do + // the work of resolving the extension, so Start doesn't need to do it again. // This is only used on Windows. - cachedLookExtensions string + cachedLookExtensions struct{ in, out string } } // A ctxResult reports the result of watching the Context associated with a @@ -436,12 +438,12 @@ func Command(name string, arg ...string) *Cmd { // Since the path is absolute, its extension should be unambiguous // and independent of cmd.Dir, and we can go ahead and cache the lookup now. // - // Note that we cannot add an extension here for relative paths, because - // cmd.Dir may be set after we return from this function and that may cause - // the command to resolve to a different extension. - lp, err := lookExtensions(name, "") - cmd.cachedLookExtensions = lp - if err != nil { + // Note that we don't cache anything here for relative paths, because + // cmd.Dir may be set after we return from this function and that may + // cause the command to resolve to a different extension. + if lp, err := lookExtensions(name, ""); err == nil { + cmd.cachedLookExtensions.in, cmd.cachedLookExtensions.out = name, lp + } else { cmd.Err = err } } @@ -642,29 +644,32 @@ func (c *Cmd) Start() error { return c.Err } lp := c.Path - if c.cachedLookExtensions != "" { - lp = c.cachedLookExtensions - } - if runtime.GOOS == "windows" && c.cachedLookExtensions == "" { - // If c.Path is relative, we had to wait until now - // to resolve it in case c.Dir was changed. - // (If it is absolute, we already resolved its extension in Command - // and shouldn't need to do so again.) - // - // Unfortunately, we cannot write the result back to c.Path because programs - // may assume that they can call Start concurrently with reading the path. - // (It is safe and non-racy to do so on Unix platforms, and users might not - // test with the race detector on all platforms; - // see https://go.dev/issue/62596.) - // - // So we will pass the fully resolved path to os.StartProcess, but leave - // c.Path as is: missing a bit of logging information seems less harmful - // than triggering a surprising data race, and if the user really cares - // about that bit of logging they can always use LookPath to resolve it. - var err error - lp, err = lookExtensions(c.Path, c.Dir) - if err != nil { - return err + if runtime.GOOS == "windows" { + if c.Path == c.cachedLookExtensions.in { + // If Command was called with an absolute path, we already resolved + // its extension and shouldn't need to do so again (provided c.Path + // wasn't set to another value between the calls to Command and Start). + lp = c.cachedLookExtensions.out + } else { + // If *Cmd was made without using Command at all, or if Command was + // called with a relative path, we had to wait until now to resolve + // it in case c.Dir was changed. + // + // Unfortunately, we cannot write the result back to c.Path because programs + // may assume that they can call Start concurrently with reading the path. + // (It is safe and non-racy to do so on Unix platforms, and users might not + // test with the race detector on all platforms; + // see https://go.dev/issue/62596.) + // + // So we will pass the fully resolved path to os.StartProcess, but leave + // c.Path as is: missing a bit of logging information seems less harmful + // than triggering a surprising data race, and if the user really cares + // about that bit of logging they can always use LookPath to resolve it. + var err error + lp, err = lookExtensions(c.Path, c.Dir) + if err != nil { + return err + } } } if c.Cancel != nil && c.ctx == nil { |