forgejo/services/archiver/archiver.go
Kyle Evans e461f0854f
[RFC] Make archival asynchronous (#11296)
* Make archival asynchronous

The prime benefit being sought here is for large archives to not
clog up the rendering process and cause unsightly proxy timeouts.
As a secondary benefit, archive-in-progress is moved out of the
way into a /tmp file so that new archival requests for the same
commit will not get fulfilled based on an archive that isn't yet
finished.

This asynchronous system is fairly primitive; request comes in, we'll
spawn off a new goroutine to handle it, then we'll mark it as done.
Status requests will see if the file exists in the final location,
and report the archival as done when it exists.

Fixes #11265

* Archive links: drop initial delay to three-quarters of a second

Some, or perhaps even most, archives will not take all that long to archive.
The archive process starts as soon as the download button is initially
clicked, so in theory they could be done quite quickly.  Drop the initial
delay down to three-quarters of a second to make it more responsive in the
common case of the archive being quickly created.

* archiver: restructure a little bit to facilitate testing

This introduces two sync.Cond pointers to the archiver package. If they're
non-nil when we go to process a request, we'll wait until signalled (at all)
to proceed. The tests will then create the sync.Cond so that it can signal
at-will and sanity-check the state of the queue at different phases.

The author believes that nil-checking these two sync.Cond pointers on every
archive processing will introduce minimal overhead with no impact on
maintainability.

* gofmt nit: no space around binary + operator

* services: archiver: appease golangci-lint, lock queueMutex

Locking/unlocking the queueMutex is allowed, but not required, for
Cond.Signal() and Cond.Broadcast().  The magic at play here is just a little
too much for golangci-lint, as we take the address of queueMutex and this is
mostly used in archiver.go; the variable still gets flagged as unused.

* archiver: tests: fix several timing nits

Once we've signaled a cond var, it may take some small amount of time for
the goroutines released to hit the spot we're wanting them to be at. Give
them an appropriate amount of time.

* archiver: tests: no underscore in var name, ungh

* archiver: tests: Test* is run in a separate context than TestMain

We must setup the mutex/cond variables at the beginning of any test that's
going to use it, or else these will be nil when the test is actually ran.

* archiver: tests: hopefully final tweak

Things got shuffled around such that we carefully build up and release
requests from the queue, so we can validate the state of the queue at each
step. Fix some assertions that no longer hold true as fallout.

* repo: Download: restore some semblance of previous behavior

When archival was made async, the GET endpoint was only useful if a previous
POST had initiated the download. This commit restores the previous behavior,
to an extent; we'll now submit the archive request there and return a
"202 Accepted" to indicate that it's processing if we didn't manage to
complete the request within ~2 seconds of submission.

This lets a client directly GET the archive, and gives them some indication
that they may attempt to GET it again at a later time.

* archiver: tests: simplify a bit further

We don't need to risk failure and use time.ParseDuration to get 2 *
time.Second.

else if isn't really necessary if the conditions are simple enough and lead
to the same result.

* archiver: tests: resolve potential source of flakiness

Increase all timeouts to 10 seconds; these aren't hard-coded sleeps, so
there's no guarantee we'll actually take that long. If we need longer to
not have a false-positive, then so be it.

While here, various assert.{Not,}Equal arguments are flipped around so that
the wording in error output reflects reality, where the expected argument is
second and actual third.

* archiver: setup infrastructure for notifying consumers of completion

This API will *not* allow consumers to subscribe to specific requests being
completed, just *any* request being completed. The caller is responsible for
determining if their request is satisfied and waiting again if needed.

* repo: archive: make GET endpoint synchronous again

If the request isn't complete, this endpoint will now submit the request and
wait for completion using the new API. This may still be susceptible to
timeouts for larger repos, but other endpoints now exist that the web
interface will use to negotiate its way through larger archive processes.

* archiver: tests: amend test to include WaitForCompletion()

This is a trivial one, so go ahead and include it.

* archiver: tests: fix test by calling NewContext()

The mutex is otherwise uninitialized, so we need to ensure that we're
actually initializing it if we plan to test it.

* archiver: tests: integrate new WaitForCompletion a little better

We can use this to wait for archives to come in, rather than spinning and
hoping with a timeout.

* archiver: tests: combine numQueued declaration with next-instruction assignment

* routers: repo: reap unused archiving flag from DownloadStatus()

This had some planned usage before, indicating whether this request
initiated the archival process or not. After several rounds of refactoring,
this use was deemed not necessary for much of anything and got boiled down
to !complete in all cases.

* services: archiver: restructure to use a channel

We now offer two forms of waiting for a request:
- WaitForCompletion: wait for completion with no timeout
- TimedWaitForCompletion: wait for completion with timeout

In both cases, we wait for the given request's cchan to close; in the latter
case, we do so with the caller-provided timeout. This completely removes the
need for busy-wait loops in Download/InitiateDownload, as it's fairly clean
to wait on a channel with timeout.

* services: archiver: use defer to unlock now that we can

This previously carried the lock into the goroutine, but an intermediate
step just added the request to archiveInProgress outside of the new
goroutine and removed the need for the goroutine to start out with it.

* Revert "archiver: tests: combine numQueued declaration with next-instruction assignment"

This reverts commit bcc5214023.

Revert "archiver: tests: integrate new WaitForCompletion a little better"

This reverts commit 9fc8bedb56.

Revert "archiver: tests: fix test by calling NewContext()"

This reverts commit 709c35685e.

Revert "archiver: tests: amend test to include WaitForCompletion()"

This reverts commit 75261f56bc.

* archiver: tests: first attempt at WaitForCompletion() tests

* archiver: tests: slight improvement, less busy-loop

Just wait for the requests to complete in order, instead of busy-waiting
with a timeout.  This is slightly less fragile.

While here, reverse the arguments of a nearby assert.Equal() so that
expected/actual are correct in any test output.

* archiver: address lint nits

* services: archiver: only close the channel once

* services: archiver: use a struct{} for the wait channel

This makes it obvious that the channel is only being used as a signal,
rather than anything useful being piped through it.

* archiver: tests: fix expectations

Move the close of the channel into doArchive() itself; notably, before these
goroutines move on to waiting on the Release cond.

The tests are adjusted to reflect that we can't WaitForCompletion() after
they've already completed, as WaitForCompletion() doesn't indicate that
they've been released from the queue yet.

* archiver: tests: set cchan to nil for comparison

* archiver: move ctx.Error's back into the route handlers

We shouldn't be setting this in a service, we should just be validating the
request that we were handed.

* services: archiver: use regex to match a hash

This makes sure we don't try and use refName as a hash when it's clearly not
one, e.g. heads/pull/foo.

* routers: repo: remove the weird /archive/status endpoint

We don't need to do this anymore, we can just continue POSTing to the
archive/* endpoint until we're told the download's complete. This avoids a
potential naming conflict, where a ref could start with "status/"

* archiver: tests: bump reasonable timeout to 15s

* archiver: tests: actually release timedReq

* archiver: tests: run through inFlight instead of manually checking

While we're here, add a test for manually re-processing an archive that's
already been complete. Re-open the channel and mark it incomplete, so that
doArchive can just mark it complete again.

* initArchiveLinks: prevent default behavior from clicking

* archiver: alias gitea's context, golang context import pending

* archiver: simplify logic, just reconstruct slices

While the previous logic was perhaps slightly more efficient, the
new variant's readability is much improved.

* archiver: don't block shutdown on waiting for archive

The technique established launches a goroutine to do the wait,
which will close a wait channel upon termination. For the timeout
case, we also send back a value indicating whether the timeout was
hit or not.

The timeouts are expected to be relatively small, but still a multi-
second delay to shutdown due to this could be unfortunate.

* archiver: simplify shutdown logic

We can just grab the shutdown channel from the graceful manager instead of
constructing a channel to halt the caller and/or pass a result back.

* Style issues

* Fix mis-merge

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Lauris BH <lauris@nix.lv>
2020-11-07 22:27:28 +02:00

310 lines
9.3 KiB
Go

// Copyright 2020 The Gitea Authors.
// All rights reserved.
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.
package archiver
import (
"io"
"io/ioutil"
"os"
"path"
"regexp"
"strings"
"sync"
"time"
"code.gitea.io/gitea/modules/base"
"code.gitea.io/gitea/modules/context"
"code.gitea.io/gitea/modules/git"
"code.gitea.io/gitea/modules/graceful"
"code.gitea.io/gitea/modules/log"
"code.gitea.io/gitea/modules/setting"
"github.com/unknwon/com"
)
// ArchiveRequest defines the parameters of an archive request, which notably
// includes the specific repository being archived as well as the commit, the
// name by which it was requested, and the kind of archive being requested.
// This is entirely opaque to external entities, though, and mostly used as a
// handle elsewhere.
type ArchiveRequest struct {
uri string
repo *git.Repository
refName string
ext string
archivePath string
archiveType git.ArchiveType
archiveComplete bool
commit *git.Commit
cchan chan struct{}
}
var archiveInProgress []*ArchiveRequest
var archiveMutex sync.Mutex
// SHA1 hashes will only go up to 40 characters, but SHA256 hashes will go all
// the way to 64.
var shaRegex = regexp.MustCompile(`^[0-9a-f]{4,64}$`)
// These facilitate testing, by allowing the unit tests to control (to some extent)
// the goroutine used for processing the queue.
var archiveQueueMutex *sync.Mutex
var archiveQueueStartCond *sync.Cond
var archiveQueueReleaseCond *sync.Cond
// GetArchivePath returns the path from which we can serve this archive.
func (aReq *ArchiveRequest) GetArchivePath() string {
return aReq.archivePath
}
// GetArchiveName returns the name of the caller, based on the ref used by the
// caller to create this request.
func (aReq *ArchiveRequest) GetArchiveName() string {
return aReq.refName + aReq.ext
}
// IsComplete returns the completion status of this request.
func (aReq *ArchiveRequest) IsComplete() bool {
return aReq.archiveComplete
}
// WaitForCompletion will wait for this request to complete, with no timeout.
// It returns whether the archive was actually completed, as the channel could
// have also been closed due to an error.
func (aReq *ArchiveRequest) WaitForCompletion(ctx *context.Context) bool {
select {
case <-aReq.cchan:
case <-ctx.Req.Context().Done():
}
return aReq.IsComplete()
}
// TimedWaitForCompletion will wait for this request to complete, with timeout
// happening after the specified Duration. It returns whether the archive is
// now complete and whether we hit the timeout or not. The latter may not be
// useful if the request is complete or we started to shutdown.
func (aReq *ArchiveRequest) TimedWaitForCompletion(ctx *context.Context, dur time.Duration) (bool, bool) {
timeout := false
select {
case <-time.After(dur):
timeout = true
case <-aReq.cchan:
case <-ctx.Req.Context().Done():
}
return aReq.IsComplete(), timeout
}
// The caller must hold the archiveMutex across calls to getArchiveRequest.
func getArchiveRequest(repo *git.Repository, commit *git.Commit, archiveType git.ArchiveType) *ArchiveRequest {
for _, r := range archiveInProgress {
// Need to be referring to the same repository.
if r.repo.Path == repo.Path && r.commit.ID == commit.ID && r.archiveType == archiveType {
return r
}
}
return nil
}
// DeriveRequestFrom creates an archival request, based on the URI. The
// resulting ArchiveRequest is suitable for being passed to ArchiveRepository()
// if it's determined that the request still needs to be satisfied.
func DeriveRequestFrom(ctx *context.Context, uri string) *ArchiveRequest {
if ctx.Repo == nil || ctx.Repo.GitRepo == nil {
log.Trace("Repo not initialized")
return nil
}
r := &ArchiveRequest{
uri: uri,
repo: ctx.Repo.GitRepo,
}
switch {
case strings.HasSuffix(uri, ".zip"):
r.ext = ".zip"
r.archivePath = path.Join(r.repo.Path, "archives/zip")
r.archiveType = git.ZIP
case strings.HasSuffix(uri, ".tar.gz"):
r.ext = ".tar.gz"
r.archivePath = path.Join(r.repo.Path, "archives/targz")
r.archiveType = git.TARGZ
default:
log.Trace("Unknown format: %s", uri)
return nil
}
r.refName = strings.TrimSuffix(r.uri, r.ext)
if !com.IsDir(r.archivePath) {
if err := os.MkdirAll(r.archivePath, os.ModePerm); err != nil {
ctx.ServerError("Download -> os.MkdirAll(archivePath)", err)
return nil
}
}
// Get corresponding commit.
var (
err error
)
if r.repo.IsBranchExist(r.refName) {
r.commit, err = r.repo.GetBranchCommit(r.refName)
if err != nil {
ctx.ServerError("GetBranchCommit", err)
return nil
}
} else if r.repo.IsTagExist(r.refName) {
r.commit, err = r.repo.GetTagCommit(r.refName)
if err != nil {
ctx.ServerError("GetTagCommit", err)
return nil
}
} else if shaRegex.MatchString(r.refName) {
r.commit, err = r.repo.GetCommit(r.refName)
if err != nil {
ctx.NotFound("GetCommit", nil)
return nil
}
} else {
ctx.NotFound("DeriveRequestFrom", nil)
return nil
}
archiveMutex.Lock()
defer archiveMutex.Unlock()
if rExisting := getArchiveRequest(r.repo, r.commit, r.archiveType); rExisting != nil {
return rExisting
}
r.archivePath = path.Join(r.archivePath, base.ShortSha(r.commit.ID.String())+r.ext)
r.archiveComplete = com.IsFile(r.archivePath)
return r
}
func doArchive(r *ArchiveRequest) {
var (
err error
tmpArchive *os.File
destArchive *os.File
)
// Close the channel to indicate to potential waiters that this request
// has finished.
defer close(r.cchan)
// It could have happened that we enqueued two archival requests, due to
// race conditions and difficulties in locking. Do one last check that
// the archive we're referring to doesn't already exist. If it does exist,
// then just mark the request as complete and move on.
if com.IsFile(r.archivePath) {
r.archiveComplete = true
return
}
// Create a temporary file to use while the archive is being built. We
// will then copy it into place (r.archivePath) once it's fully
// constructed.
tmpArchive, err = ioutil.TempFile("", "archive")
if err != nil {
log.Error("Unable to create a temporary archive file! Error: %v", err)
return
}
defer func() {
tmpArchive.Close()
os.Remove(tmpArchive.Name())
}()
if err = r.commit.CreateArchive(graceful.GetManager().ShutdownContext(), tmpArchive.Name(), git.CreateArchiveOpts{
Format: r.archiveType,
Prefix: setting.Repository.PrefixArchiveFiles,
}); err != nil {
log.Error("Download -> CreateArchive "+tmpArchive.Name(), err)
return
}
// Now we copy it into place
if destArchive, err = os.Create(r.archivePath); err != nil {
log.Error("Unable to open archive " + r.archivePath)
return
}
_, err = io.Copy(destArchive, tmpArchive)
destArchive.Close()
if err != nil {
log.Error("Unable to write archive " + r.archivePath)
return
}
// Block any attempt to finalize creating a new request if we're marking
r.archiveComplete = true
}
// ArchiveRepository satisfies the ArchiveRequest being passed in. Processing
// will occur in a separate goroutine, as this phase may take a while to
// complete. If the archive already exists, ArchiveRepository will not do
// anything. In all cases, the caller should be examining the *ArchiveRequest
// being returned for completion, as it may be different than the one they passed
// in.
func ArchiveRepository(request *ArchiveRequest) *ArchiveRequest {
// We'll return the request that's already been enqueued if it has been
// enqueued, or we'll immediately enqueue it if it has not been enqueued
// and it is not marked complete.
archiveMutex.Lock()
defer archiveMutex.Unlock()
if rExisting := getArchiveRequest(request.repo, request.commit, request.archiveType); rExisting != nil {
return rExisting
}
if request.archiveComplete {
return request
}
request.cchan = make(chan struct{})
archiveInProgress = append(archiveInProgress, request)
go func() {
// Wait to start, if we have the Cond for it. This is currently only
// useful for testing, so that the start and release of queued entries
// can be controlled to examine the queue.
if archiveQueueStartCond != nil {
archiveQueueMutex.Lock()
archiveQueueStartCond.Wait()
archiveQueueMutex.Unlock()
}
// Drop the mutex while we process the request. This may take a long
// time, and it's not necessary now that we've added the reequest to
// archiveInProgress.
doArchive(request)
if archiveQueueReleaseCond != nil {
archiveQueueMutex.Lock()
archiveQueueReleaseCond.Wait()
archiveQueueMutex.Unlock()
}
// Purge this request from the list. To do so, we'll just take the
// index at which we ended up at and swap the final element into that
// position, then chop off the now-redundant final element. The slice
// may have change in between these two segments and we may have moved,
// so we search for it here. We could perhaps avoid this search
// entirely if len(archiveInProgress) == 1, but we should verify
// correctness.
archiveMutex.Lock()
defer archiveMutex.Unlock()
idx := -1
for _idx, req := range archiveInProgress {
if req == request {
idx = _idx
break
}
}
if idx == -1 {
log.Error("ArchiveRepository: Failed to find request for removal.")
return
}
archiveInProgress = append(archiveInProgress[:idx], archiveInProgress[idx+1:]...)
}()
return request
}