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3be8cf71dd
* Pass Go context down to Renderers This is useful for cancellation or tracing. * Add tracing spans to app Also log things like number of nodes in Map, total number of reports.
82 lines
1.6 KiB
Go
82 lines
1.6 KiB
Go
package render
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import (
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"context"
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"fmt"
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"math/rand"
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"sync"
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"github.com/bluele/gcache"
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"github.com/weaveworks/scope/report"
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)
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// renderCache is keyed on the combination of Memoiser and report
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// id. It contains promises of report.Nodes, which result from
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// rendering the report with the Memoiser's renderer.
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//
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// The use of promises ensures that in the absence of cache evictions
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// a memoiser will only ever render a report once, even when Render()
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// is invoked concurrently.
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var renderCache = gcache.New(100).LRU().Build()
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type memoise struct {
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sync.Mutex
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Renderer
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id string
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}
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// Memoise wraps the renderer in a loving embrace of caching.
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func Memoise(r Renderer) Renderer {
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if _, ok := r.(*memoise); ok {
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return r // fixpoint
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}
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return &memoise{
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Renderer: r,
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id: fmt.Sprintf("%x", rand.Int63()),
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}
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}
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// Render produces a set of Nodes given a Report. Ideally, it just
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// retrieves a promise from the cache and returns its value, otherwise
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// it stores a new promise and fulfils it by calling through to
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// m.Renderer.
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func (m *memoise) Render(ctx context.Context, rpt report.Report) Nodes {
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key := fmt.Sprintf("%s-%s", rpt.ID, m.id)
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m.Lock()
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v, err := renderCache.Get(key)
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if err == nil {
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m.Unlock()
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return v.(*promise).Get()
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}
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promise := newPromise()
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renderCache.Set(key, promise)
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m.Unlock()
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output := m.Renderer.Render(ctx, rpt)
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promise.Set(output)
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return output
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}
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type promise struct {
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val Nodes
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done chan struct{}
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}
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func newPromise() *promise {
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return &promise{done: make(chan struct{})}
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}
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func (p *promise) Set(val Nodes) {
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p.val = val
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close(p.done)
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}
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func (p *promise) Get() Nodes {
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<-p.done
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return p.val
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}
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