diff options
| author | Russ Cox <rsc@golang.org> | 2019-04-29 21:29:16 -0400 |
|---|---|---|
| committer | Russ Cox <rsc@golang.org> | 2019-04-30 13:12:48 +0000 |
| commit | 8e28cd19acc43437e7ccec25dd0572afd6b77f8a (patch) | |
| tree | 220de68fb2e082d32d5551c93183bab979b5b48e /src | |
| parent | 203e18883726409205df4af11935d6393ed9ad52 (diff) | |
| download | go-8e28cd19acc43437e7ccec25dd0572afd6b77f8a.tar.xz | |
cmd/go/internal/modfetch: fix concurrent read/write race in modfetch
On Windows systems, the failure rate for cmd/go's TestScript/mod_concurrent
is somewhere around 3-10% without this change. With the change, I have yet
to see a failure.
Fixes #31744.
Change-Id: Ib321ebb9556dd8438086cf329dfa083a9e051732
Reviewed-on: https://go-review.googlesource.com/c/go/+/174439
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Diffstat (limited to 'src')
| -rw-r--r-- | src/cmd/go/internal/modfetch/sumdb.go | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/src/cmd/go/internal/modfetch/sumdb.go b/src/cmd/go/internal/modfetch/sumdb.go index b01aad8333..ebfb95b716 100644 --- a/src/cmd/go/internal/modfetch/sumdb.go +++ b/src/cmd/go/internal/modfetch/sumdb.go @@ -233,7 +233,15 @@ func (*dbClient) WriteConfig(file string, old, new []byte) error { // which will be deleted by "go clean -modcache". func (*dbClient) ReadCache(file string) ([]byte, error) { targ := filepath.Join(PkgMod, "download/cache/sumdb", file) - return lockedfile.Read(targ) + data, err := lockedfile.Read(targ) + // lockedfile.Write does not atomically create the file with contents. + // There is a moment between file creation and locking the file for writing, + // during which the empty file can be locked for reading. + // Treat observing an empty file as file not found. + if err == nil && len(data) == 0 { + err = &os.PathError{Op: "read", Path: targ, Err: os.ErrNotExist} + } + return data, err } // WriteCache updates cached lookups or tiles. |