Add SQLite support, fix un-thread-safe DB caches, small performance f… (#172)

* Add SQLite support, fix un-thread-safe DB caches, small performance fixes

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

* add SQLite licenses to README

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

* appease the linter, and fix my dumbass-ery

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

* make requested changes

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

* add back comment

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

internal/cache/status.go

@@ -0,0 +1,106 @@
+package cache
+
+import (
+	"sync"
+
+	"github.com/ReneKroon/ttlcache"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+)
+
+// statusCache is a wrapper around ttlcache.Cache to provide URL and URI lookups for gtsmodel.Status
+type StatusCache struct {
+	cache *ttlcache.Cache   // map of IDs -> cached statuses
+	urls  map[string]string // map of status URLs -> IDs
+	uris  map[string]string // map of status URIs -> IDs
+	mutex sync.Mutex
+}
+
+// newStatusCache returns a new instantiated statusCache object
+func NewStatusCache() *StatusCache {
+	c := StatusCache{
+		cache: ttlcache.NewCache(),
+		urls:  make(map[string]string, 100),
+		uris:  make(map[string]string, 100),
+		mutex: sync.Mutex{},
+	}
+
+	// Set callback to purge lookup maps on expiration
+	c.cache.SetExpirationCallback(func(key string, value interface{}) {
+		status := value.(*gtsmodel.Status)
+
+		c.mutex.Lock()
+		delete(c.urls, status.URL)
+		delete(c.uris, status.URI)
+		c.mutex.Unlock()
+	})
+
+	return &c
+}
+
+// GetByID attempts to fetch a status from the cache by its ID
+func (c *StatusCache) GetByID(id string) (*gtsmodel.Status, bool) {
+	c.mutex.Lock()
+	status, ok := c.getByID(id)
+	c.mutex.Unlock()
+	return status, ok
+}
+
+// GetByURL attempts to fetch a status from the cache by its URL
+func (c *StatusCache) GetByURL(url string) (*gtsmodel.Status, bool) {
+	// Perform safe ID lookup
+	c.mutex.Lock()
+	id, ok := c.urls[url]
+
+	// Not found, unlock early
+	if !ok {
+		c.mutex.Unlock()
+		return nil, false
+	}
+
+	// Attempt status lookup
+	status, ok := c.getByID(id)
+	c.mutex.Unlock()
+	return status, ok
+}
+
+// GetByURI attempts to fetch a status from the cache by its URI
+func (c *StatusCache) GetByURI(uri string) (*gtsmodel.Status, bool) {
+	// Perform safe ID lookup
+	c.mutex.Lock()
+	id, ok := c.uris[uri]
+
+	// Not found, unlock early
+	if !ok {
+		c.mutex.Unlock()
+		return nil, false
+	}
+
+	// Attempt status lookup
+	status, ok := c.getByID(id)
+	c.mutex.Unlock()
+	return status, ok
+}
+
+// getByID performs an unsafe (no mutex locks) lookup of status by ID
+func (c *StatusCache) getByID(id string) (*gtsmodel.Status, bool) {
+	v, ok := c.cache.Get(id)
+	if !ok {
+		return nil, false
+	}
+	return v.(*gtsmodel.Status), true
+}
+
+// Put places a status in the cache
+func (c *StatusCache) Put(status *gtsmodel.Status) {
+	if status == nil || status.ID == "" ||
+		status.URL == "" ||
+		status.URI == "" {
+		panic("invalid status")
+	}
+
+	c.mutex.Lock()
+	c.cache.Set(status.ID, status)
+	c.urls[status.URL] = status.ID
+	c.uris[status.URI] = status.ID
+	c.mutex.Unlock()
+}