[lxc-devel] [lxd/master] support canceling with parallel downloads

[albertodonato on Github]

The following pull request was submitted through Github.
It can be accessed and reviewed at: https://github.com/lxc/lxd/pull/3918

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=== Description (from pull-request) ===
Fixes #3917 

From 59e42cfb65698248a1d77e7eb08f9aae6e957898 Mon Sep 17 00:00:00 2001
From: Alberto Donato <alberto.don...@canonical.com>
Date: Mon, 9 Oct 2017 12:15:18 +0200
Subject: [PATCH] support canceling with parallel downloads

Signed-off-by: Alberto Donato <alberto.don...@canonical.com>
---
 lxd/daemon_images.go      |  2 +-
 shared/cancel/canceler.go | 22 +++++++++++++++-------
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/lxd/daemon_images.go b/lxd/daemon_images.go
index 06bb5fd4a..b3a3e12c8 100644
--- a/lxd/daemon_images.go
+++ b/lxd/daemon_images.go
@@ -360,7 +360,7 @@ func (d *Daemon) ImageDownload(op *operation, server 
string, protocol string, ce
 
        var canceler *cancel.Canceler
        if op != nil {
-               canceler = &cancel.Canceler{}
+               canceler = cancel.NewCanceler()
                op.canceler = canceler
        }
 
diff --git a/shared/cancel/canceler.go b/shared/cancel/canceler.go
index 83c58992f..6a27347a0 100644
--- a/shared/cancel/canceler.go
+++ b/shared/cancel/canceler.go
@@ -7,20 +7,28 @@ import (
 
 // A struct to track canceleation
 type Canceler struct {
-       chCancel chan struct{}
+       reqChCancel map[*http.Request]chan struct{}
+}
+
+func NewCanceler() *Canceler {
+       c := Canceler{}
+       c.reqChCancel = make(map[*http.Request]chan struct{})
+       return &c
 }
 
 func (c *Canceler) Cancelable() bool {
-       return c.chCancel != nil
+       return len(c.reqChCancel) > 0
 }
 
 func (c *Canceler) Cancel() error {
-       if c.chCancel == nil {
+       if !c.Cancelable() {
                return fmt.Errorf("This operation cannot be canceled at this 
time")
        }
 
-       close(c.chCancel)
-       c.chCancel = nil
+       for req, ch := range c.reqChCancel {
+               close(ch)
+               delete(c.reqChCancel, req)
+       }
        return nil
 }
 
@@ -28,14 +36,14 @@ func CancelableDownload(c *Canceler, client *http.Client, 
req *http.Request) (*h
        chDone := make(chan bool)
        chCancel := make(chan struct{})
        if c != nil {
-               c.chCancel = chCancel
+               c.reqChCancel[req] = chCancel
        }
        req.Cancel = chCancel
 
        go func() {
                <-chDone
                if c != nil {
-                       c.chCancel = nil
+                       delete(c.reqChCancel, req)
                }
        }()
 

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