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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
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cibuild	wgengine/magicsock: increase legacy ping timeout again	4 years ago
cmpver	util/cmpver: move into OSS from corp repo.	4 years ago
deephash	util/deephash: improve cycle detection (#2470)	3 years ago
dnsname	util/dnsname: make ToFQDN take exactly 0 or 1 allocs for everything.	4 years ago
endian	util/endian: add Native variable to get the platform's native binary.ByteOrder	4 years ago
groupmember	cmd/tailscale/web: add support for QNAP	4 years ago
jsonutil	util/jsonutil: new package	4 years ago
lineread	util/lineread: add docs to Reader	4 years ago
osshare	ipn/ipnlocal: add file sharing to windows shell	4 years ago
pidowner	util/pidowner: add missing copyright header	4 years ago
racebuild	util/racebuild: add package to export a race-is-enabled const	4 years ago
systemd	util/systemd: explicitly check for os.ErrNotExist from sdnotify	4 years ago
uniq	util/uniq: add new package	4 years ago
winutil	net/dns: do not run wsl.exe as LocalSystem	3 years ago