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Profile: multithread getdict! (redo of #43805) #43816

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Feb 3, 2022
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Profile: multithread getdict! (redo of #43805) #43816

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eaf99c0
multithread getdict!
IanButterworth Jan 15, 2022
1a360ac
move `update_stackframes_callback[]` to sequential loop
IanButterworth Jan 16, 2022
d4af208
remove channel
IanButterworth Jan 16, 2022
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32 changes: 23 additions & 9 deletions stdlib/Profile/src/Profile.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -349,19 +349,33 @@ function getdict(data::Vector{UInt})
end

function getdict!(dict::LineInfoDict, data::Vector{UInt})
for ip in data
# Lookup is expensive, so do it only once per ip.
haskey(dict, UInt64(ip)) && continue
st = lookup(convert(Ptr{Cvoid}, ip))
# To correct line numbers for moving code, put it in the form expected by
# Base.update_stackframes_callback[]
stn = map(x->(x, 1), st)
try Base.invokelatest(Base.update_stackframes_callback[], stn) catch end
dict[UInt64(ip)] = map(first, stn)
# we don't want metadata here as we're just looking up ips
unique_ips = unique(has_meta(data) ? strip_meta(data) : data)
n_unique_ips = length(unique_ips)
n_unique_ips == 0 && return dict
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The expensive part is the lookup. Can't you just

iplookups = similar(unique_ips, Vector{StackFrame})
Threads.@threads for i = 1:n_unique_ips
    iplookups[i] = _lookup_corrected(unique_ips[i])
end

and then stash in the Dict in single-threaded mode?

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I didn't use @threads because @jpsamaroo pointed out @threads would get blocked if any thread is doing something that isn't yielding.

Though, regarding just putting it into a buffer, I was thinking that would be memory inefficient, but maybe I'm wrong because the dict is empty to start with..

I'll try removing the channel stuff.

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Not a big deal, but you're not using the limited-capacity aspect of the Channel at all, so this is really just a glorified array-store. If you store by the index of the ip you don't have to worry about races.Indeed, you could replace the @threads with @spawned blocks.

chnl = Channel{Pair{UInt64,Vector{StackFrame}}}(n_unique_ips) do ch
# don't use `Threads.@threads` here because we don't want this to get blocked
@sync for ips_part in Iterators.partition(unique_ips, div(n_unique_ips, Threads.nthreads(), RoundUp))
Threads.@spawn begin
for ip in ips_part
put!(ch, UInt64(ip) => _lookup_corrected(ip))
end
end
end
end
foreach(v -> dict[first(v)] = last(v), chnl)
return dict
end

function _lookup_corrected(ip::UInt)
st = lookup(convert(Ptr{Cvoid}, ip))
# To correct line numbers for moving code, put it in the form expected by
# Base.update_stackframes_callback[]
stn = map(x->(x, 1), st)
try Base.invokelatest(Base.update_stackframes_callback[], stn) catch end
return map(first, stn)
end
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"""
flatten(btdata::Vector, lidict::LineInfoDict) -> (newdata::Vector{UInt64}, newdict::LineInfoFlatDict)
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