• Josh Bleecher Snyder's avatar
    context: lazily initialize cancelCtx done channel · 986768de
    Josh Bleecher Snyder authored
    This CL reduces allocations when a context
    created with WithCancel either
    
    (1) never has its Done channel used or
    (2) gets cancelled before its Done channel is used
    
    This is not uncommon. Many contexts are created
    for tasks that end up not using them.
    
    name                                                old time/op    new time/op    delta
    ContextCancelTree/depth=1/Root=Background-8            112ns ± 2%      74ns ± 1%  -34.03%  (p=0.000 n=17+18)
    ContextCancelTree/depth=1/Root=OpenCanceler-8          601ns ± 3%     544ns ± 1%   -9.56%  (p=0.000 n=20+20)
    ContextCancelTree/depth=1/Root=ClosedCanceler-8        367ns ± 4%     257ns ± 1%  -30.01%  (p=0.000 n=20+20)
    ContextCancelTree/depth=10/Root=Background-8          2.91µs ± 2%    2.87µs ± 0%   -1.38%  (p=0.000 n=20+18)
    ContextCancelTree/depth=10/Root=OpenCanceler-8        4.36µs ± 2%    4.26µs ± 1%   -2.34%  (p=0.000 n=20+18)
    ContextCancelTree/depth=10/Root=ClosedCanceler-8      2.02µs ± 2%    1.51µs ± 1%  -25.18%  (p=0.000 n=19+19)
    ContextCancelTree/depth=100/Root=Background-8         30.5µs ± 6%    30.5µs ± 1%     ~     (p=0.941 n=20+20)
    ContextCancelTree/depth=100/Root=OpenCanceler-8       39.8µs ± 1%    41.1µs ± 1%   +3.15%  (p=0.000 n=18+19)
    ContextCancelTree/depth=100/Root=ClosedCanceler-8     17.8µs ± 1%    13.9µs ± 1%  -21.61%  (p=0.000 n=18+20)
    ContextCancelTree/depth=1000/Root=Background-8         302µs ± 1%     313µs ± 0%   +3.62%  (p=0.000 n=20+18)
    ContextCancelTree/depth=1000/Root=OpenCanceler-8       412µs ± 2%     427µs ± 1%   +3.55%  (p=0.000 n=18+19)
    ContextCancelTree/depth=1000/Root=ClosedCanceler-8     178µs ± 1%     139µs ± 1%  -21.80%  (p=0.000 n=19+17)
    
    name                                                old alloc/op   new alloc/op   delta
    ContextCancelTree/depth=1/Root=Background-8             176B ± 0%       80B ± 0%  -54.55%  (p=0.000 n=20+20)
    ContextCancelTree/depth=1/Root=OpenCanceler-8           544B ± 0%      448B ± 0%  -17.65%  (p=0.000 n=20+20)
    ContextCancelTree/depth=1/Root=ClosedCanceler-8         352B ± 0%      160B ± 0%  -54.55%  (p=0.000 n=20+20)
    ContextCancelTree/depth=10/Root=Background-8          3.49kB ± 0%    3.39kB ± 0%   -2.75%  (p=0.000 n=20+20)
    ContextCancelTree/depth=10/Root=OpenCanceler-8        3.86kB ± 0%    3.76kB ± 0%   -2.49%  (p=0.000 n=20+20)
    ContextCancelTree/depth=10/Root=ClosedCanceler-8      1.94kB ± 0%    0.88kB ± 0%  -54.55%  (p=0.000 n=20+20)
    ContextCancelTree/depth=100/Root=Background-8         36.6kB ± 0%    36.5kB ± 0%   -0.26%  (p=0.000 n=20+20)
    ContextCancelTree/depth=100/Root=OpenCanceler-8       37.0kB ± 0%    36.9kB ± 0%   -0.26%  (p=0.000 n=20+20)
    ContextCancelTree/depth=100/Root=ClosedCanceler-8     17.8kB ± 0%     8.1kB ± 0%  -54.55%  (p=0.000 n=20+20)
    ContextCancelTree/depth=1000/Root=Background-8         368kB ± 0%     368kB ± 0%   -0.03%  (p=0.000 n=20+20)
    ContextCancelTree/depth=1000/Root=OpenCanceler-8       368kB ± 0%     368kB ± 0%   -0.03%  (p=0.000 n=20+20)
    ContextCancelTree/depth=1000/Root=ClosedCanceler-8     176kB ± 0%      80kB ± 0%  -54.55%  (p=0.000 n=20+20)
    
    name                                                old allocs/op  new allocs/op  delta
    ContextCancelTree/depth=1/Root=Background-8             3.00 ± 0%      2.00 ± 0%  -33.33%  (p=0.000 n=20+20)
    ContextCancelTree/depth=1/Root=OpenCanceler-8           8.00 ± 0%      7.00 ± 0%  -12.50%  (p=0.000 n=20+20)
    ContextCancelTree/depth=1/Root=ClosedCanceler-8         6.00 ± 0%      4.00 ± 0%  -33.33%  (p=0.000 n=20+20)
    ContextCancelTree/depth=10/Root=Background-8            48.0 ± 0%      47.0 ± 0%   -2.08%  (p=0.000 n=20+20)
    ContextCancelTree/depth=10/Root=OpenCanceler-8          53.0 ± 0%      52.0 ± 0%   -1.89%  (p=0.000 n=20+20)
    ContextCancelTree/depth=10/Root=ClosedCanceler-8        33.0 ± 0%      22.0 ± 0%  -33.33%  (p=0.000 n=20+20)
    ContextCancelTree/depth=100/Root=Background-8            498 ± 0%       497 ± 0%   -0.20%  (p=0.000 n=20+20)
    ContextCancelTree/depth=100/Root=OpenCanceler-8          503 ± 0%       502 ± 0%   -0.20%  (p=0.000 n=20+20)
    ContextCancelTree/depth=100/Root=ClosedCanceler-8        303 ± 0%       202 ± 0%  -33.33%  (p=0.000 n=20+20)
    ContextCancelTree/depth=1000/Root=Background-8         5.00k ± 0%     5.00k ± 0%   -0.02%  (p=0.000 n=20+20)
    ContextCancelTree/depth=1000/Root=OpenCanceler-8       5.00k ± 0%     5.00k ± 0%   -0.02%  (p=0.000 n=20+20)
    ContextCancelTree/depth=1000/Root=ClosedCanceler-8     3.00k ± 0%     2.00k ± 0%  -33.33%  (p=0.000 n=20+20)
    
    Change-Id: Ibd7a0c3d5c847861cf1497f8fead34329413d26d
    Reviewed-on: https://go-review.googlesource.com/34979
    Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    Reviewed-by: 's avatarBrad Fitzpatrick <bradfitz@golang.org>
    Reviewed-by: 's avatarSameer Ajmani <sameer@golang.org>
    986768de
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