From f06c6fdcbf24ba56fc16e69069734d4436010622 Mon Sep 17 00:00:00 2001
From: Varun Patil <varunpatil@ucla.edu>
Date: Sun, 26 Feb 2023 15:08:02 -0800
Subject: [PATCH] Revert "x-img: simplify logic of cache"

This reverts commit d86e9406d38238eac08a9eaa995193a148b379bf.
---
 src/components/frame/XImg.vue | 70 +++++++++++++++++++++++++++--------
 1 file changed, 55 insertions(+), 15 deletions(-)

diff --git a/src/components/frame/XImg.vue b/src/components/frame/XImg.vue
index c2790b6a..efe3b0b6 100644
--- a/src/components/frame/XImg.vue
+++ b/src/components/frame/XImg.vue
@@ -6,7 +6,7 @@
 import { defineComponent } from "vue";
 import { fetchImage } from "./XImgCache";
 
-const BLOB_CACHE: { [src: string]: string } = {};
+const BLOB_CACHE: { [src: string]: [number, string] } = {};
 const BLANK_IMG =
   "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7";
 
@@ -26,11 +26,13 @@ export default defineComponent({
   data: () => {
     return {
       dataSrc: BLANK_IMG,
+      isDestroyed: false,
     };
   },
 
   watch: {
-    src() {
+    src(newSrc, oldSrc) {
+      this.cleanup(oldSrc);
       this.loadImage();
     },
   },
@@ -39,9 +41,15 @@ export default defineComponent({
     this.loadImage();
   },
 
+  beforeDestroy() {
+    this.cleanup(this.src);
+    this.isDestroyed = true;
+  },
+
   methods: {
     async loadImage() {
       if (!this.src) return;
+      this.isDestroyed = false;
 
       // Just set src if not http
       if (this.src.startsWith("data:") || this.src.startsWith("blob:")) {
@@ -51,20 +59,35 @@ export default defineComponent({
 
       // Fetch image with axios
       try {
-        const src = this.src;
-        if (BLOB_CACHE[src]) {
-          this.dataSrc = BLOB_CACHE[src];
-          return;
-        }
+        // Use BLOB from cache assuming it exists
+        const usedCache = (src: string) => {
+          if (BLOB_CACHE[src]) {
+            this.dataSrc = BLOB_CACHE[src][1];
+            BLOB_CACHE[src][0]++;
+            return true;
+          }
+          return false;
+        };
 
-        const newBlob = await fetchImage(src);
-        if (this.src === src) {
-          const blobUrl = URL.createObjectURL(newBlob);
-          BLOB_CACHE[src] = this.dataSrc = blobUrl;
-          setTimeout(() => {
-            if (BLOB_CACHE[src] === blobUrl) delete BLOB_CACHE[src];
-            URL.revokeObjectURL(blobUrl);
-          }, 60 * 1000);
+        // Check if the blob cache exists
+        if (!usedCache(this.src)) {
+          const src = this.src;
+          const newBlob = URL.createObjectURL(await fetchImage(src));
+          if (this.src !== src || this.isDestroyed) {
+            URL.revokeObjectURL(newBlob); // the src has changed, abort
+            return;
+          }
+
+          // Check if the blob cache exists now
+          // In this case, someone else already created the blob
+          // Free up the current blob and use the existing one instead
+          if (usedCache(src)) {
+            URL.revokeObjectURL(newBlob);
+          } else {
+            // Create new blob cache entry
+            this.dataSrc = newBlob;
+            BLOB_CACHE[src] = [1, this.dataSrc];
+          }
         }
       } catch (error) {
         this.dataSrc = BLANK_IMG;
@@ -76,6 +99,23 @@ export default defineComponent({
       if (this.dataSrc === BLANK_IMG) return;
       this.$emit("load", this.dataSrc);
     },
+
+    async cleanup(src: string) {
+      if (!src) return;
+
+      // Wait for 1s before collecting garbage
+      await new Promise((r) => setTimeout(r, 1000));
+
+      // Clean up blob cache
+      const cache = BLOB_CACHE[src];
+      if (!cache) return;
+
+      // Remove blob from cache
+      if (--cache[0] <= 0) {
+        URL.revokeObjectURL(cache[1]);
+        delete BLOB_CACHE[src];
+      }
+    },
   },
 });
 </script>