58 Commits (7a77a2edf16f756975f360209f97fbb140b07f0e)

Author	SHA1	Message	Date
Joe Tsai	94a4f701c2	all: use reflect.TypeFor now available in Go 1.22 (#11078) ... Updates #cleanup Signed-off-by: Joe Tsai <joetsai@digital-static.net>	10 months ago
Joe Tsai	60657ac83f	util/deephash: tighten up SelfHasher API (#11012) ... Providing a hash.Block512 is an implementation detail of how deephash works today, but providing an opaque type with mostly equivalent API (i.e., HashUint8, HashBytes, etc. methods) is still sensible. Thus, define a public Hasher type that exposes exactly the API that an implementation of SelfHasher would want to call. This gives us freedom to change the hashing algorithm of deephash at some point in the future. Also, this type is likely going to be called by types that are going to memoize their own hash results, we additionally add a HashSum method to simplify this use case. Add documentation to SelfHasher on how a type might implement it. Updates: corp#16409 Signed-off-by: Joe Tsai <joetsai@digital-static.net>	10 months ago
Joe Tsai	84f8311bcd	util/deephash: document pathological deephash behavior (#11010) ... Updates #cleanup Signed-off-by: Joe Tsai <joetsai@digital-static.net>	10 months ago
Tom DNetto	2aeef4e610	util/deephash: implement SelfHasher to allow types to hash themselves ... Updates: corp#16409 Signed-off-by: Tom DNetto <tom@tailscale.com>	10 months ago
Brad Fitzpatrick	4af22f3785	util/deephash: add IncludeFields, ExcludeFields HasherForType Options ... Updates tailscale/corp#6198 Change-Id: Iafc18c5b947522cf07a42a56f35c0319cc7b1c94 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	1 year ago
Will Norris	71029cea2d	all: update copyright and license headers ... This updates all source files to use a new standard header for copyright and license declaration. Notably, copyright no longer includes a date, and we now use the standard SPDX-License-Identifier header. This commit was done almost entirely mechanically with perl, and then some minimal manual fixes. Updates #6865 Signed-off-by: Will Norris <will@tailscale.com>	2 years ago
Josh Soref	d4811f11a0	all: fix spelling mistakes ... Signed-off-by: Josh Soref <2119212+jsoref@users.noreply.github.com>	2 years ago
Andrew Dunham	4b996ad5e3	util/deephash: add AppendSum method (#5768) ... This method can be used to obtain the hex-formatted deephash.Sum instance without allocations. Signed-off-by: Andrew Dunham <andrew@du.nham.ca>	2 years ago
Joe Tsai	7e40071571	util/deephash: handle slice edge-cases (#5471) ... It is unclear whether the lack of checking nil-ness of slices was an oversight or a deliberate feature. Lacking a comment, the assumption is that this was an oversight. Also, expand the logic to perform cycle detection for recursive slices. We do this on a per-element basis since a slice is semantically equivalent to a list of pointers. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	9bf13fc3d1	util/deephash: remove getTypeInfo (#5469) ... Add a new lookupTypeHasher function that is just a cached front-end around the makeTypeHasher function. We do not need to worry about the recursive type cycle issue that made getTypeInfo more complicated since makeTypeHasher is not directly recursive. All calls to itself happen lazily through a sync.Once upon first use. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	ab7e6f3f11	util/deephash: require pointer in API (#5467) ... The entry logic of Hash has extra complexity to make sure we always have an addressable value on hand. If not, we heap allocate the input. For this reason we document that there are performance benefits to always providing a pointer. Rather than documenting this, just enforce it through generics. Also, delete the unused HasherForType function. It's an interesting use of generics, but not well tested. We can resurrect it from code history if there's a need for it. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	c5b1565337	util/deephash: move pointer and interface logic to separate function (#5465) ... This helps pprof better identify which Go kinds take the most time since the kind is always in the function name. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	d2e2d8438b	util/deephash: move map logic to separate function (#5464) ... This helps pprof better identify which Go kinds take the most time since the kind is always in the function name. There is a minor adjustment where we hash the length of the map to be more on the cautious side. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	23c3831ff9	util/deephash: coalesce struct logic (#5466) ... Rather than having two copies []fieldInfo, just maintain one and perform merging in the same pass. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	296b008b9f	util/deephash: move array and slice logic to separate function (#5463) ... This helps pprof better identify which Go kinds take the most time since the kind is always in the function name. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	31bf3874d6	util/deephash: use unsafe.Pointer instead of reflect.Value (#5459) ... Use of reflect.Value.SetXXX panics if the provided argument was obtained from an unexported struct field. Instead, pass an unsafe.Pointer around and convert to a reflect.Value when necessary (i.e., for maps and interfaces). Converting from unsafe.Pointer to reflect.Value guarantees that none of the read-only bits will be populated. When running in race mode, we attach type information to the pointer so that we can type check every pointer operation. This also type-checks that direct memory hashing is within the valid range of a struct value. We add test cases that previously caused deephash to panic, but now pass. Performance: name old time/op new time/op delta Hash 14.1µs ± 1% 14.1µs ± 1% ~ (p=0.590 n=10+9) HashPacketFilter 2.53µs ± 2% 2.44µs ± 1% -3.79% (p=0.000 n=9+10) TailcfgNode 1.45µs ± 1% 1.43µs ± 0% -1.36% (p=0.000 n=9+9) HashArray 318ns ± 2% 318ns ± 2% ~ (p=0.541 n=10+10) HashMapAcyclic 32.9µs ± 1% 31.6µs ± 1% -4.16% (p=0.000 n=10+9) There is a slight performance gain due to the use of unsafe.Pointer over reflect.Value methods. Also, passing an unsafe.Pointer (1 word) on the stack is cheaper than passing a reflect.Value (3 words). Performance gains are diminishing since SHA-256 hashing now dominates the runtime. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	70f9fc8c7a	util/deephash: rely on direct memory hashing for primitive kinds (#5457) ... Rather than separate functions to hash each kind, just rely on the fact that these are direct memory hashable, thus simplifying the code. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	531ccca648	util/deephash: delete slow path (#5423) ... Every implementation of typeHasherFunc always returns true, which implies that the slow path is no longer executed. Delete it. h.hashValueWithType(v, ti, ...) is deleted as it is equivalent to: ti.hasher()(h, v) h.hashValue(v, ...) is deleted as it is equivalent to: ti := getTypeInfo(v.Type()) ti.hasher()(h, v) Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	3fc8683585	util/deephash: expand fast-path capabilities (#5404) ... Add support for maps and interfaces to the fast path. Add cycle-detection to the pointer handling logic. This logic is mostly copied from the slow path. A future commit will delete the slow path once the fast path never falls back to the slow path. Performance: name old time/op new time/op delta Hash-24 18.5µs ± 1% 14.9µs ± 2% -19.52% (p=0.000 n=10+10) HashPacketFilter-24 2.54µs ± 1% 2.60µs ± 1% +2.19% (p=0.000 n=10+10) HashMapAcyclic-24 31.6µs ± 1% 30.5µs ± 1% -3.42% (p=0.000 n=9+8) TailcfgNode-24 1.44µs ± 2% 1.43µs ± 1% ~ (p=0.171 n=10+10) HashArray-24 324ns ± 1% 324ns ± 2% ~ (p=0.425 n=9+9) The additional cycle detection logic doesn't incur much slow down since it only activates if a type is recursive, which does not apply for any of the types that we care about. There is a notable performance boost since we switch from the fath path to the slow path less often. Most notably, a struct with a field that could not be handled by the fast path would previously cause the entire struct to go through the slow path. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	d32700c7b2	util/deephash: specialize for netip.Addr and drop AppendTo support (#5402) ... There are 5 types that we care about that implement AppendTo: key.DiscoPublic key.NodePublic netip.Prefix netipx.IPRange netip.Addr The key types are thin wrappers around [32]byte and are memory hashable. The netip.Prefix and netipx.IPRange types are thin wrappers over netip.Addr and are hashable by default if netip.Addr is hashable. The netip.Addr type is the only one with a complex structure where the default behavior of deephash does not hash it correctly due to the presence of the intern.Value type. Drop support for AppendTo and instead add specialized hashing for netip.Addr that would be semantically equivalent to == on the netip.Addr values. The AppendTo support was already broken prior to this change. It was fully removed (intentionally or not) in #4870. It was partially restored in #4858 for the fast path, but still broken in the slow path. Just drop support for it altogether. This does mean we lack any ability for types to self-hash themselves. In the future we can add support for types that implement: interface { DeepHash() Sum } Test and fuzz cases were added for the relevant types that used to rely on the AppendTo method. FuzzAddr has been executed on 1 billion samples without issues. Signed-off-by: Joe Tsai joetsai@digital-static.net	2 years ago
Joe Tsai	03f7e4e577	util/hashx: move from sha256x (#5388)	2 years ago
Joe Tsai	f061d20c9d	util/sha256x: rename Hash as Block512 (#5351) ... Rename Hash as Block512 to indicate that this is a general-purpose hash.Hash for any algorithm that operates on 512-bit block sizes. While we rename the package as hashx in this commit, a subsequent commit will move the sha256x package to hashx. This is done separately to avoid confusing git. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	44d62b65d0	util/deephash: move typeIsRecursive and canMemHash to types.go (#5386) ... Also, rename canMemHash to typeIsMemHashable to be consistent. There are zero changes to the semantics. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	d53eb6fa11	util/deephash: simplify typeIsRecursive (#5385) ... Any type that is memory hashable must not be recursive since there are definitely no pointers involved to make a cycle. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	23ec3c104a	util/deephash: remove unused stack slice in typeIsRecursive (#5363) ... No operation ever reads from this variable. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	c200229f9e	util/deephash: simplify canMemHash (#5384) ... Put the t.Size() == 0 check first since this is applicable in all cases. Drop the last struct field conditional since this is covered by the sumFieldSize check at the end. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	32a1a3d1c0	util/deephash: avoid variadic argument for Update (#5372) ... Hashing []any is slow since hashing of interfaces is slow. Hashing of interfaces is slow since we pessimistically assume that cycles can occur through them and start cycle tracking. Drop the variadic signature of Update and fix callers to pass in an anonymous struct so that we are hashing concrete types near the root of the value tree. Signed-off-by: Joe Tsai <joetsai@digital-static.net> Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	548fa63e49	util/deephash: use binary encoding of time.Time (#5352) ... Formatting a time.Time as RFC3339 is slow. See https://go.dev/issue/54093 Now that we have efficient hashing of fixed-width integers, just hash the time.Time as a binary value. Performance: Hash-24 19.0µs ± 1% 18.6µs ± 1% -2.03% (p=0.000 n=10+9) TailcfgNode-24 1.79µs ± 1% 1.40µs ± 1% -21.74% (p=0.000 n=10+9) Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	1f7479466e	util/deephash: use sha256x (#5339) ... Switch deephash to use sha256x.Hash. We add sha256x.HashString to efficiently hash a string. It uses unsafe under the hood to convert a string to a []byte. We also modify sha256x.Hash to export the underlying hash.Hash for testing purposes so that we can intercept all hash.Hash calls. Performance: name old time/op new time/op delta Hash-24 19.8µs ± 1% 19.2µs ± 1% -3.01% (p=0.000 n=10+10) HashPacketFilter-24 2.61µs ± 0% 2.53µs ± 1% -3.01% (p=0.000 n=8+10) HashMapAcyclic-24 31.3µs ± 1% 29.8µs ± 0% -4.80% (p=0.000 n=10+9) TailcfgNode-24 1.83µs ± 1% 1.82µs ± 2% ~ (p=0.305 n=10+10) HashArray-24 344ns ± 2% 323ns ± 1% -6.02% (p=0.000 n=9+10) The performance gains is not as dramatic as sha256x over sha256 due to: 1. most of the hashing already occurring through the direct memory hashing logic, and 2. what does not go through direct memory hashing is slowed down by reflect. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	77a92f326d	util/deephash: avoid using sync.Pool for reflect.MapIter (#5333) ... In Go 1.19, the reflect.Value.MapRange method uses "function outlining" so that the allocation of reflect.MapIter is inlinable by the caller. If the iterator doesn't escape the caller, it can be stack allocated. See https://go.dev/cl/400675 Performance: name old time/op new time/op delta HashMapAcyclic-24 31.9µs ± 2% 32.1µs ± 1% ~ (p=0.075 n=10+10) name old alloc/op new alloc/op delta HashMapAcyclic-24 0.00B 0.00B ~ (all equal) Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Joe Tsai	539c5e44c5	util/deephash: always keep values addressable (#5328) ... The logic of deephash is both simpler and easier to reason about if values are always addressable. In Go, the composite kinds are slices, arrays, maps, structs, interfaces, pointers, channels, and functions, where we define "composite" as a Go value that encapsulates some other Go value (e.g., a map is a collection of key-value entries). In the cases of pointers and slices, the sub-values are always addressable. In the cases of arrays and structs, the sub-values are always addressable if and only if the parent value is addressable. In the case of maps and interfaces, the sub-values are never addressable. To make them addressable, we need to copy them onto the heap. For the purposes of deephash, we do not care about channels and functions. For all non-composite kinds (e.g., strings and ints), they are only addressable if obtained from one of the composite kinds that produce addressable values (i.e., pointers, slices, addressable arrays, and addressable structs). A non-addressible, non-composite kind can be made addressable by allocating it on the heap, obtaining a pointer to it, and dereferencing it. Thus, if we can ensure that values are addressable at the entry points, and shallow copy sub-values whenever we encounter an interface or map, then we can ensure that all values are always addressable and assume such property throughout all the logic. Performance: name old time/op new time/op delta Hash-24 21.5µs ± 1% 19.7µs ± 1% -8.29% (p=0.000 n=9+9) HashPacketFilter-24 2.61µs ± 1% 2.62µs ± 0% +0.29% (p=0.037 n=10+9) HashMapAcyclic-24 30.8µs ± 1% 30.9µs ± 1% ~ (p=0.400 n=9+10) TailcfgNode-24 1.84µs ± 1% 1.84µs ± 2% ~ (p=0.928 n=10+10) HashArray-24 324ns ± 2% 332ns ± 2% +2.45% (p=0.000 n=10+10) Signed-off-by: Joe Tsai <joetsai@digital-static.net>	2 years ago
Brad Fitzpatrick	116f55ff66	all: gofmt for Go 1.19 ... Updates #5210 Change-Id: Ib02cd5e43d0a8db60c1f09755a8ac7b140b670be Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	2 years ago
Brad Fitzpatrick	04cf46a762	util/deephash: fix unexported time.Time hashing ... Updates tailscale/corp#6311 Change-Id: I33cd7e4040966261c2f2eb3d32f29936aeb7f632 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	2 years ago
Brad Fitzpatrick	2a22ea3e83	util/deephash: generate type-specific hasher funcs ... name old time/op new time/op delta Hash-8 71.1µs ± 2% 71.5µs ± 1% ~ (p=0.114 n=9+8) HashPacketFilter-8 8.39µs ± 1% 4.83µs ± 2% -42.38% (p=0.000 n=8+9) HashMapAcyclic-8 56.2µs ± 1% 56.9µs ± 2% +1.17% (p=0.035 n=10+9) TailcfgNode-8 6.49µs ± 2% 3.54µs ± 1% -45.37% (p=0.000 n=9+9) HashArray-8 729ns ± 2% 566ns ± 3% -22.30% (p=0.000 n=10+10) name old alloc/op new alloc/op delta Hash-8 24.0B ± 0% 24.0B ± 0% ~ (all equal) HashPacketFilter-8 24.0B ± 0% 24.0B ± 0% ~ (all equal) HashMapAcyclic-8 0.00B 0.00B ~ (all equal) TailcfgNode-8 0.00B 0.00B ~ (all equal) HashArray-8 0.00B 0.00B ~ (all equal) name old allocs/op new allocs/op delta Hash-8 1.00 ± 0% 1.00 ± 0% ~ (all equal) HashPacketFilter-8 1.00 ± 0% 1.00 ± 0% ~ (all equal) HashMapAcyclic-8 0.00 0.00 ~ (all equal) TailcfgNode-8 0.00 0.00 ~ (all equal) HashArray-8 0.00 0.00 ~ (all equal) Change-Id: I34c4e786e748fe60280646d40cc63a2adb2ea6fe Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	2 years ago
Brad Fitzpatrick	35782f891d	util/deephash: add canMemHash func + typeInfo property ... Currently unused. (breaking up a bigger change) Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	2 years ago
Brad Fitzpatrick	8c5c87be26	util/deephash: fix collisions between different types ... Updates #4883 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	2 years ago
Brad Fitzpatrick	757ecf7e80	util/deephash: fix map hashing when key & element have the same type ... Regression from 09afb8e35b, in which the same reflect.Value scratch value was being used as the map iterator copy destination. Also: make nil and empty maps hash differently, add test. Fixes #4871 Co-authored-by: Josh Bleecher Snyder <josharian@gmail.com> Change-Id: I67f42524bc81f694c1b7259d6682200125ea4a66 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	2 years ago
Brad Fitzpatrick	f31588786f	util/deephash: don't track cycles on non-recursive types ... name old time/op new time/op delta Hash-8 67.3µs ±20% 76.5µs ±16% ~ (p=0.143 n=10+10) HashMapAcyclic-8 63.0µs ± 2% 56.3µs ± 1% -10.65% (p=0.000 n=10+8) TailcfgNode-8 9.18µs ± 2% 6.52µs ± 3% -28.96% (p=0.000 n=9+10) HashArray-8 732ns ± 3% 709ns ± 1% -3.21% (p=0.000 n=10+10) name old alloc/op new alloc/op delta Hash-8 24.0B ± 0% 24.0B ± 0% ~ (all equal) HashMapAcyclic-8 0.00B 0.00B ~ (all equal) TailcfgNode-8 0.00B 0.00B ~ (all equal) HashArray-8 0.00B 0.00B ~ (all equal) name old allocs/op new allocs/op delta Hash-8 1.00 ± 0% 1.00 ± 0% ~ (all equal) HashMapAcyclic-8 0.00 0.00 ~ (all equal) TailcfgNode-8 0.00 0.00 ~ (all equal) HashArray-8 0.00 0.00 ~ (all equal) Change-Id: I28642050d837dff66b2db54b2b0e6d272a930be8 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	2 years ago
Brad Fitzpatrick	36ea837736	util/deephash: fix map hashing to actually hash elements ... Fixes #4868 Change-Id: I574fd139cb7f7033dd93527344e6aa0e625477c7 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	2 years ago
Josh Bleecher Snyder	0868329936	all: use any instead of interface{} ... My favorite part of generics. Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>	3 years ago
Josh Bleecher Snyder	97a01b7b17	util/deephash: remove Tailscale toolchain compatibility shim ... The future is now. Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>	3 years ago
slowy07	ac0353e982	fix: typo spelling grammar ... Signed-off-by: slowy07 <slowy.arfy@gmail.com>	3 years ago
Joe Tsai	9d0c86b6ec	util/deephash: remove unnecessary formatting for structs and slices (#2571) ... The index for every struct field or slice element and the number of fields for the struct is unncessary. The hashing of Go values is unambiguous because every type (except maps) encodes in a parsable manner. So long as we know the type information, we could theoretically decode every value (except for maps). At a high level: * numbers are encoded as fixed-width records according to precision. * strings (and AppendTo output) are encoded with a fixed-width length, followed by the contents of the buffer. * slices are prefixed by a fixed-width length, followed by the encoding of each value. So long as we know the type of each element, we could theoretically decode each element. * arrays are encoded just like slices, but elide the length since it is determined from the Go type. * maps are encoded first with a byte indicating whether it is a cycle. If a cycle, it is followed by a fixed-width index for the pointer, otherwise followed by the SHA-256 hash of its contents. The encoding of maps is not decodeable, but a SHA-256 hash is sufficient to avoid ambiguities. * interfaces are encoded first with a byte indicating whether it is nil. If not nil, it is followed by a fixed-width index for the type, and then the encoding for the underlying value. Having the type be encoded first ensures that the value could theoretically be decoded next. * pointers are encoded first with a byte indicating whether it is 1) nil, 2) a cycle, or 3) newly seen. If a cycle, it is followed by a fixed-width index for the pointer. If newly seen, it is followed by the encoding for the pointed-at value. Removing unnecessary details speeds up hashing: name old time/op new time/op delta Hash-8 76.0µs ± 1% 55.8µs ± 2% -26.62% (p=0.000 n=10+10) HashMapAcyclic-8 61.9µs ± 0% 62.0µs ± 0% ~ (p=0.666 n=9+9) TailcfgNode-8 10.2µs ± 1% 7.5µs ± 1% -26.90% (p=0.000 n=10+9) HashArray-8 1.07µs ± 1% 0.70µs ± 1% -34.67% (p=0.000 n=10+9) Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago
Joe Tsai	d8fbce7eef	util/deephash: hash uint{8,16,32,64} explicitly (#2502) ... Instead of hashing the humanly formatted forms of a number, hash the native machine bits of the integers themselves. There is a small performance gain for this: name old time/op new time/op delta Hash-8 75.7µs ± 1% 76.0µs ± 2% ~ (p=0.315 n=10+9) HashMapAcyclic-8 63.1µs ± 3% 61.3µs ± 1% -2.77% (p=0.000 n=10+10) TailcfgNode-8 10.3µs ± 1% 10.2µs ± 1% -1.48% (p=0.000 n=10+10) HashArray-8 1.07µs ± 1% 1.05µs ± 1% -1.79% (p=0.000 n=10+10) Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago
Joe Tsai	01d4dd331d	util/deephash: simplify hasher.hashMap (#2503) ... The swapping of bufio.Writer between hasher and mapHasher is subtle. Just embed a hasher in mapHasher to avoid complexity here. No notable change in performance: name old time/op new time/op delta Hash-8 76.7µs ± 1% 77.0µs ± 1% ~ (p=0.182 n=9+10) HashMapAcyclic-8 62.4µs ± 1% 62.5µs ± 1% ~ (p=0.315 n=10+9) TailcfgNode-8 10.3µs ± 1% 10.3µs ± 1% -0.62% (p=0.004 n=10+9) HashArray-8 1.07µs ± 1% 1.06µs ± 1% -0.98% (p=0.001 n=8+9) Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago
Joe Tsai	d145c594ad	util/deephash: improve cycle detection (#2470) ... The previous algorithm used a map of all visited pointers. The strength of this approach is that it quickly prunes any nodes that we have ever visited before. The detriment of the approach is that pruning is heavily dependent on the order that pointers were visited. This is especially relevant for hashing a map where map entries are visited in a non-deterministic manner, which would cause the map hash to be non-deterministic (which defeats the point of a hash). This new algorithm uses a stack of all visited pointers, similar to how github.com/google/go-cmp performs cycle detection. When we visit a pointer, we push it onto the stack, and when we leave a pointer, we pop it from the stack. Before visiting a pointer, we first check whether the pointer exists anywhere in the stack. If yes, then we prune the node. The detriment of this approach is that we may hash a node more often than before since we do not prune as aggressively. The set of visited pointers up until any node is only the path of nodes up to that node and not any other pointers that may have been visited elsewhere. This provides us deterministic hashing regardless of visit order. We can now delete hashMapFallback and associated complexity, which only exists because the previous approach was non-deterministic in the presence of cycles. This fixes a failure of the old algorithm where obviously different values are treated as equal because the pruning was too aggresive. See https://github.com/tailscale/tailscale/issues/2443#issuecomment-883653534 The new algorithm is slightly slower since it prunes less aggresively: name old time/op new time/op delta Hash-8 66.1µs ± 1% 68.8µs ± 1% +4.09% (p=0.000 n=19+19) HashMapAcyclic-8 63.0µs ± 1% 62.5µs ± 1% -0.76% (p=0.000 n=18+19) TailcfgNode-8 9.79µs ± 2% 9.88µs ± 1% +0.95% (p=0.000 n=19+17) HashArray-8 643ns ± 1% 653ns ± 1% +1.64% (p=0.000 n=19+19) However, a slower but more correct algorithm seems more favorable than a faster but incorrect algorithm. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago
Joe Tsai	d666bd8533	util/deephash: disambiguate hashing of AppendTo (#2483) ... Prepend size to AppendTo output. Fixes #2443 Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago
Joe Tsai	23ad028414	util/deephash: include type as part of hash for interfaces (#2476) ... A Go interface may hold any number of different concrete types. Just because two underlying values hash to the same thing does not mean the two values are identical if they have different concrete types. As such, include the type in the hash.	3 years ago
Joe Tsai	a5fb8e0731	util/deephash: introduce deliberate instability (#2477) ... Seed the hash upon first use with the current time. This ensures that the stability of the hash is bounded within the lifetime of one program execution. Hopefully, this prevents future bugs where someone assumes that this hash is stable. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago
Joe Tsai	9a0c8bdd20	util/deephash: make hash type opaque ... The fact that Hash returns a [sha256.Size]byte leaks details about the underlying hash implementation. This could very well be any other hashing algorithm with a possible different block size. Abstract this implementation detail away by declaring an opaque type that is comparable. While we are changing the signature of UpdateHash, rename it to just Update to reduce stutter (e.g., deephash.Update). Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago