Improve content map, memory cache and dependency resolution

TODO(bep) improve commit message.

Hugo has always been a active user of in-memory caches, but before this commit we did nothing to control the memory usage.

One failing example would be loading lots of big JSON data files and unmarshal them via `transform.Unmarshal`.

This commit consolidates all these caches into one single LRU cache with an eviction strategy that also considers used vs. available memory.

Hugo will try to limit its memory usage to 1/4 or total system memory, but this can be controlled with the `HUGO_MEMORYLIMIT` environment variable (a float value representing Gigabytes).

A natural next step after this would be to use this cache for `.Content`.

Fixes gohugoio#8307
Fixes gohugoio#8498
Fixes gohugoio#8927
Fixes gohugoio#9192
Fixes gohugoio#9189
Fixes gohugoio#7425
Fixes gohugoio#7437
Fixes gohugoio#7436
Fixes gohugoio#7882
Updates gohugoio#7544
Fixes gohugoio#9224
Fixes gohugoio#9324

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+    "autoHide.autoHidePanel": false
+}

benchbep.sh

@@ -1 +1 @@
-gobench -package=./hugolib -bench="BenchmarkSiteNew/Deep_content_tree"
+gobench --package ./hugolib --bench "BenchmarkSiteNew/Regular_Deep" -base v0.89.4

cache/filecache/filecache.go

@@ -15,6 +15,7 @@ package filecache
 
 import (
 	"bytes"
+	"context"
 	"errors"
 	"io"
 	"io/ioutil"
@@ -163,7 +164,7 @@ func (c *Cache) ReadOrCreate(id string,
 // GetOrCreate tries to get the file with the given id from cache. If not found or expired, create will
 // be invoked and the result cached.
 // This method is protected by a named lock using the given id as identifier.
-func (c *Cache) GetOrCreate(id string, create func() (io.ReadCloser, error)) (ItemInfo, io.ReadCloser, error) {
+func (c *Cache) GetOrCreate(ctx context.Context, id string, create func() (io.ReadCloser, error)) (ItemInfo, io.ReadCloser, error) {
 	id = cleanID(id)
 
 	c.nlocker.Lock(id)

cache/filecache/filecache_test.go

@@ -14,6 +14,7 @@
 package filecache
 
 import (
+	"context"
 	"errors"
 	"fmt"
 	"io"
@@ -134,7 +135,7 @@ dir = ":cacheDir/c"
 
 		for _, ca := range []*Cache{caches.ImageCache(), caches.AssetsCache(), caches.GetJSONCache(), caches.GetCSVCache()} {
 			for i := 0; i < 2; i++ {
-				info, r, err := ca.GetOrCreate("a", rf("abc"))
+				info, r, err := ca.GetOrCreate(context.TODO(), "a", rf("abc"))
 				c.Assert(err, qt.IsNil)
 				c.Assert(r, qt.Not(qt.IsNil))
 				c.Assert(info.Name, qt.Equals, "a")
@@ -152,7 +153,7 @@ dir = ":cacheDir/c"
 				c.Assert(err, qt.IsNil)
 				c.Assert(string(b), qt.Equals, "abc")
 
-				_, r, err = ca.GetOrCreate("a", rf("bcd"))
+				_, r, err = ca.GetOrCreate(context.TODO(), "a", rf("bcd"))
 				c.Assert(err, qt.IsNil)
 				b, _ = ioutil.ReadAll(r)
 				r.Close()
@@ -229,7 +230,7 @@ dir = "/cache/c"
 				ca := caches.Get(cacheName)
 				c.Assert(ca, qt.Not(qt.IsNil))
 				filename, data := filenameData(i)
-				_, r, err := ca.GetOrCreate(filename, func() (io.ReadCloser, error) {
+				_, r, err := ca.GetOrCreate(context.TODO(), filename, func() (io.ReadCloser, error) {
 					return hugio.ToReadCloser(strings.NewReader(data)), nil
 				})
 				c.Assert(err, qt.IsNil)