vole
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A free and open-source forge that lives in your Git repo.
| 1 | package git |
| 2 | |
| 3 | // Writers of one ref take turns. These tests hold the two things that makes true: |
| 4 | // concurrent writes all land, and they land without each writer re-reading the |
| 5 | // tree it is about to lose. The attempt count is read from GIT_TRACE, the same |
| 6 | // way TestCommitFilesStaysProportionalToTheChange counts processes: every |
| 7 | // `update-ref` is one attempt, won or lost. |
| 8 | |
| 9 | import ( |
| 10 | "bytes" |
| 11 | "fmt" |
| 12 | "os" |
| 13 | "path/filepath" |
| 14 | "strings" |
| 15 | "sync" |
| 16 | "testing" |
| 17 | ) |
| 18 | |
| 19 | func lockRepo(t *testing.T) (*Repo, string) { |
| 20 | t.Helper() |
| 21 | dir := filepath.Join(t.TempDir(), "r.git") |
| 22 | if err := InitBare(dir, "main"); err != nil { |
| 23 | t.Fatal(err) |
| 24 | } |
| 25 | g := Open(dir) |
| 26 | ref := "refs/heads/main" |
| 27 | if _, err := CommitFiles(g, ref, func(files map[string][]byte) error { |
| 28 | // Enough unrelated content that a full read is worth losing, which is what |
| 29 | // the retry used to pay for. |
| 30 | for i := 0; i < 200; i++ { |
| 31 | files[fmt.Sprintf("issues/%03d/issue.md", i)] = []byte("seed\n") |
| 32 | } |
| 33 | return nil |
| 34 | }, "seed", "test"); err != nil { |
| 35 | t.Fatal(err) |
| 36 | } |
| 37 | return g, ref |
| 38 | } |
| 39 | |
| 40 | // TestCommitFilesSerializesWriters is the regression test for the retry storm: with |
| 41 | // writers taking turns, every write needs exactly one attempt, and every write is in |
| 42 | // the tree afterwards. |
| 43 | func TestCommitFilesSerializesWriters(t *testing.T) { |
| 44 | g, ref := lockRepo(t) |
| 45 | const writers, each = 8, 4 |
| 46 | const total = writers * each |
| 47 | |
| 48 | trace := filepath.Join(t.TempDir(), "git.trace") |
| 49 | traced := *g |
| 50 | traced.ExtraEnv = append(traced.ExtraEnv, "GIT_TRACE="+trace) |
| 51 | |
| 52 | var wg sync.WaitGroup |
| 53 | errs := make(chan error, total) |
| 54 | for w := 0; w < writers; w++ { |
| 55 | wg.Add(1) |
| 56 | go func(w int) { |
| 57 | defer wg.Done() |
| 58 | for i := 0; i < each; i++ { |
| 59 | path := fmt.Sprintf("issues/w%02d-%d/issue.md", w, i) |
| 60 | if _, err := CommitFiles(&traced, ref, func(files map[string][]byte) error { |
| 61 | files[path] = []byte(fmt.Sprintf("w%d i%d\n", w, i)) |
| 62 | return nil |
| 63 | }, "write", "test"); err != nil { |
| 64 | errs <- err |
| 65 | return |
| 66 | } |
| 67 | } |
| 68 | }(w) |
| 69 | } |
| 70 | wg.Wait() |
| 71 | close(errs) |
| 72 | for err := range errs { |
| 73 | t.Fatal(err) |
| 74 | } |
| 75 | |
| 76 | data, err := os.ReadFile(trace) |
| 77 | if err != nil { |
| 78 | t.Fatal(err) |
| 79 | } |
| 80 | attempts := bytes.Count(data, []byte("update-ref")) |
| 81 | if attempts > total { |
| 82 | t.Fatalf("%d writes from %d goroutines took %d attempts: writers are not taking turns", |
| 83 | total, writers, attempts) |
| 84 | } |
| 85 | |
| 86 | // Nothing was lost on the way. |
| 87 | files, err := g.FlatTree(ref) |
| 88 | if err != nil { |
| 89 | t.Fatal(err) |
| 90 | } |
| 91 | for w := 0; w < writers; w++ { |
| 92 | for i := 0; i < each; i++ { |
| 93 | path := fmt.Sprintf("issues/w%02d-%d/issue.md", w, i) |
| 94 | want := fmt.Sprintf("w%d i%d\n", w, i) |
| 95 | if got := string(files[path]); got != want { |
| 96 | t.Fatalf("%s = %q, want %q", path, got, want) |
| 97 | } |
| 98 | } |
| 99 | } |
| 100 | } |
| 101 | |
| 102 | // A write that fails still gives the lock back, or the branch would be stuck for |
| 103 | // every writer after it. |
| 104 | func TestCommitFilesReleasesTheLockAfterAFailure(t *testing.T) { |
| 105 | g, ref := lockRepo(t) |
| 106 | _, err := CommitFiles(g, ref, func(files map[string][]byte) error { |
| 107 | return fmt.Errorf("nothing to do") |
| 108 | }, "failed", "test") |
| 109 | if err == nil { |
| 110 | t.Fatal("a failing mutation was reported as a commit") |
| 111 | } |
| 112 | if _, err := CommitFiles(g, ref, func(files map[string][]byte) error { |
| 113 | files["issues/after/issue.md"] = []byte("after\n") |
| 114 | return nil |
| 115 | }, "after", "test"); err != nil { |
| 116 | t.Fatalf("the write after a failure waited forever or failed: %v", err) |
| 117 | } |
| 118 | } |
| 119 | |
| 120 | // Two refs are two queues: a slow write on one must not hold up the other, which is |
| 121 | // what makes the lock per-ref rather than per-repository. |
| 122 | func TestCommitFilesLocksEachRefSeparately(t *testing.T) { |
| 123 | g, ref := lockRepo(t) |
| 124 | other := "refs/heads/pages" |
| 125 | started := make(chan struct{}) |
| 126 | release := make(chan struct{}) |
| 127 | done := make(chan error, 1) |
| 128 | go func() { |
| 129 | _, err := CommitFiles(g, ref, func(files map[string][]byte) error { |
| 130 | close(started) |
| 131 | <-release |
| 132 | files["issues/slow/issue.md"] = []byte("slow\n") |
| 133 | return nil |
| 134 | }, "slow", "test") |
| 135 | done <- err |
| 136 | }() |
| 137 | <-started |
| 138 | if _, err := CommitFiles(g, other, func(files map[string][]byte) error { |
| 139 | files["index.html"] = []byte("hello\n") |
| 140 | return nil |
| 141 | }, "pages", "test"); err != nil { |
| 142 | t.Fatalf("a write to another ref was held up: %v", err) |
| 143 | } |
| 144 | close(release) |
| 145 | if err := <-done; err != nil { |
| 146 | t.Fatal(err) |
| 147 | } |
| 148 | } |
| 149 | |
| 150 | // The retry loop is still there for a writer that went around the lock, and still |
| 151 | // finishes. A ref moved by hand between the read and the compare-and-swap is the |
| 152 | // only way to reach it once writers take turns. |
| 153 | func TestCommitFilesStillRetriesARefMovedByHand(t *testing.T) { |
| 154 | g, ref := lockRepo(t) |
| 155 | before, err := g.RevParse(ref) |
| 156 | if err != nil { |
| 157 | t.Fatal(err) |
| 158 | } |
| 159 | // A commit that does not move the tree, so a write that rebases onto it is |
| 160 | // still the write the caller asked for. |
| 161 | out, err := g.Run(nil, "rev-parse", "--verify", before+"^{tree}") |
| 162 | if err != nil { |
| 163 | t.Fatal(err) |
| 164 | } |
| 165 | tree := strings.TrimSpace(string(out)) |
| 166 | side, err := g.CommitTree(tree, before, "hand") |
| 167 | if err != nil { |
| 168 | t.Fatal(err) |
| 169 | } |
| 170 | moved := false |
| 171 | _, err = CommitFiles(g, ref, func(files map[string][]byte) error { |
| 172 | if !moved { |
| 173 | // Stand in for `git update-ref` run by someone else: the lock cannot see |
| 174 | // it, so the first compare-and-swap must lose. |
| 175 | moved = true |
| 176 | if err := g.UpdateRef(ref, side); err != nil { |
| 177 | return err |
| 178 | } |
| 179 | } |
| 180 | files["issues/racing/issue.md"] = []byte("racing\n") |
| 181 | return nil |
| 182 | }, "write", "test") |
| 183 | if err != nil { |
| 184 | t.Fatalf("a write that lost one compare-and-swap gave up: %v", err) |
| 185 | } |
| 186 | files, err := g.FlatTree(ref) |
| 187 | if err != nil { |
| 188 | t.Fatal(err) |
| 189 | } |
| 190 | if string(files["issues/racing/issue.md"]) != "racing\n" { |
| 191 | t.Fatal("the write that lost the race is not in the tree") |
| 192 | } |
| 193 | if head, err := g.RevParse(ref); err != nil || head == side { |
| 194 | t.Fatalf("the branch is still where the hand edit left it: %s, %v", head, err) |
| 195 | } |
| 196 | } |
| 197 |