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Cache: fix multi-process race condition on macOS #15351

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merged 1 commit into from
Apr 19, 2023
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Cache: fix multi-process race condition on macOS #15351

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41 changes: 23 additions & 18 deletions lib/std/Build/Cache.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -434,24 +434,29 @@ pub const Manifest = struct {
}
}
} else {
if (self.cache.manifest_dir.createFile(&manifest_file_path, .{
.read = true,
.truncate = false,
.lock = .Exclusive,
.lock_nonblocking = self.want_shared_lock,
})) |manifest_file| {
self.manifest_file = manifest_file;
self.have_exclusive_lock = true;
} else |err| switch (err) {
// There are no dir components, so you would think that this was
// unreachable, however we have observed on macOS two processes racing
// to do openat() with O_CREAT manifest in ENOENT.
error.WouldBlock, error.FileNotFound => {
self.manifest_file = try self.cache.manifest_dir.openFile(&manifest_file_path, .{
.lock = .Shared,
});
},
else => |e| return e,
while (true) {
if (self.cache.manifest_dir.createFile(&manifest_file_path, .{
.read = true,
.truncate = false,
.lock = .Exclusive,
.lock_nonblocking = self.want_shared_lock,
})) |manifest_file| {
self.manifest_file = manifest_file;
self.have_exclusive_lock = true;
break;
} else |err| switch (err) {
error.WouldBlock => {
self.manifest_file = try self.cache.manifest_dir.openFile(&manifest_file_path, .{
.lock = .Shared,
});
break;
},
// There are no dir components, so you would think that this was
// unreachable, however we have observed on macOS two processes racing
// to do openat() with O_CREAT manifest in ENOENT.
error.FileNotFound => continue,
else => |e| return e,
}
}
}

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