Commit 7ff42eff91

@@ -528,6 +528,43 @@ pub const Manifest = struct {
                     };
                     break;
                 },
+                error.FileNotFound => {
+                    // There are no dir components, so the only possibility
+                    // should be that the directory behind the handle has been
+                    // deleted, however we have observed on macOS two processes
+                    // racing to do openat() with O_CREAT manifest in ENOENT.
+                    //
+                    // As a workaround, we retry with exclusive=true which
+                    // disambiguates by returning EEXIST, indicating original
+                    // failure was a race, or ENOENT, indicating deletion of
+                    // the directory of our open handle.
+                    if (builtin.os.tag != .macos) {
+                        self.diagnostic = .{ .manifest_create = error.FileNotFound };
+                        return error.CacheCheckFailed;
+                    }
+
+                    if (self.cache.manifest_dir.createFile(&manifest_file_path, .{
+                        .read = true,
+                        .truncate = false,
+                        .lock = .exclusive,
+                        .lock_nonblocking = self.want_shared_lock,
+                        .exclusive = true,
+                    })) |manifest_file| {
+                        self.manifest_file = manifest_file;
+                        self.have_exclusive_lock = true;
+                        break;
+                    } else |excl_err| switch (excl_err) {
+                        error.WouldBlock, error.PathAlreadyExists => continue,
+                        error.FileNotFound => {
+                            self.diagnostic = .{ .manifest_create = error.FileNotFound };
+                            return error.CacheCheckFailed;
+                        },
+                        else => |e| {
+                            self.diagnostic = .{ .manifest_create = e };
+                            return error.CacheCheckFailed;
+                        },
+                    }
+                },
                 else => |e| {
                     self.diagnostic = .{ .manifest_create = e };
                     return error.CacheCheckFailed;

@@ -770,7 +770,7 @@ fn failWithCacheError(s: *Step, man: *const Build.Cache.Manifest, err: Build.Cac
             },
         },
         error.OutOfMemory => return error.OutOfMemory,
-        error.InvalidFormat => return s.fail("failed check cache: invalid manifest file format", .{}),
+        error.InvalidFormat => return s.fail("failed to check cache: invalid manifest file format", .{}),
     }
 }
 

@@ -1541,6 +1541,8 @@ pub const OpenError = error{
     /// * One of the path components does not exist.
     /// * Cwd was used, but cwd has been deleted.
     /// * The path associated with the open directory handle has been deleted.
+    /// * On macOS, multiple processes or threads raced to create the same file
+    ///   with `O.EXCL` set to `false`.
     FileNotFound,
 
     /// The path exceeded `max_path_bytes` bytes.

@@ -136,12 +136,34 @@ pub fn astGenFile(
             error.NoDevice => unreachable, // it's not a pipe
             error.WouldBlock => unreachable, // not asking for non-blocking I/O
             error.FileNotFound => {
-                // Since there are no dir components this could only occur if
-                // `zir_dir` is deleted after the compiler process obtains an
-                // open directory handle.
-                std.process.fatal("cache directory '{}' unexpectedly removed during compiler execution", .{
-                    cache_directory,
-                });
+                // There are no dir components, so the only possibility should
+                // be that the directory behind the handle has been deleted,
+                // however we have observed on macOS two processes racing to do
+                // openat() with O_CREAT manifest in ENOENT.
+                //
+                // As a workaround, we retry with exclusive=true which
+                // disambiguates by returning EEXIST, indicating original
+                // failure was a race, or ENOENT, indicating deletion of the
+                // directory of our open handle.
+                if (builtin.os.tag != .macos) {
+                    std.process.fatal("cache directory '{}' unexpectedly removed during compiler execution", .{
+                        cache_directory,
+                    });
+                }
+                break zir_dir.createFile(&hex_digest, .{
+                    .read = true,
+                    .truncate = false,
+                    .lock = lock,
+                    .exclusive = true,
+                }) catch |excl_err| switch (excl_err) {
+                    error.PathAlreadyExists => continue,
+                    error.FileNotFound => {
+                        std.process.fatal("cache directory '{}' unexpectedly removed during compiler execution", .{
+                            cache_directory,
+                        });
+                    },
+                    else => |e| return e,
+                };
             },
 
             else => |e| return e, // Retryable errors are handled at callsite.

@@ -2069,7 +2069,7 @@ pub fn update(comp: *Compilation, main_progress_node: std.Progress.Node) !void {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.InvalidFormat => return comp.setMiscFailure(
                     .check_whole_cache,
-                    "failed check cache: invalid manifest file format",
+                    "failed to check cache: invalid manifest file format",
                     .{},
                 ),
             };