compress/flate: add Reset method to let callers avoid garbage

[bradfitz]

Related to issue #6136, flate.NewWriter generates a lot of garbage which can't be
controlled by the calling application.

Options:

-- internal memory reuse in the flate package
-- Reset method (like bufio.Reader and bufio.Writer)
-- let buffers be passed in

Attachments:

1. k0EYnXJ_LT.0.svg (15027 bytes)

[bradfitz]

Comment 1:

Each call to flate.NewWriter allocates 1.4 MB of memory, and Close doesn't reuse any of
it.

[rsc]

Comment 2:

Reset method please.
(Rationale: Having the reset method means that the buffer is attached to the Writer, not
magically moving around, so it gives the caller more control and also keeps the reuse
local to a specific package.)

[rsc]

Comment 3:

I wish it did generate a "log of garbage". That would make things easier.

[bradfitz]

Comment 4:

This issue was updated by revision c7d352c.

TestOver65kFiles spends all its time garbage collecting.
Removing the 1.4 MB of allocations per each of the 65k
files brings this from 34 seconds to 0.23 seconds.
R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/12894043

[robpike]

Comment 5:

Looks fixed to me. Reopen if you disagree.

Status changed to Fixed.

[bradfitz]

Comment 6:

Per comment #2, this bug focused to be about adding a Reset method on flate.Writer so
callers can avoid 1.4 MB of garbage per writer if it affects them.

Owner changed to @bradfitz.

Status changed to Accepted.

[remyoudompheng]

Comment 7:

Should we create separate issues for compress/zlib and compress/gzip ? Most people never
use compress/flate directly, and the most common demand is probably Resetting a
gzip.Writer.

[remyoudompheng]

Comment 8:

This issue was closed by revision f5f0e40.

Status changed to Fixed.

[bradfitz]

Comment 9:

This issue was updated by revision db12f9d.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/13435043