From 1cf7e1e5cde8f4d660179a527b4706b6d32c1e1a Mon Sep 17 00:00:00 2001
From: Chris Loer <chris.loer@gmail.com>
Date: Thu, 13 Dec 2018 14:23:04 -0800
Subject: [PATCH] Hack in pool for ArrayBuffers used by StructArray.

---
 src/data/bucket/symbol_bucket.js | 18 ++++++++++
 src/source/worker_tile.js        |  8 +++++
 src/util/struct_array.js         | 60 ++++++++++++++++++++++++++++++--
 3 files changed, 84 insertions(+), 2 deletions(-)

diff --git a/src/data/bucket/symbol_bucket.js b/src/data/bucket/symbol_bucket.js
index d03e8302fb2..11d470504af 100644
--- a/src/data/bucket/symbol_bucket.js
+++ b/src/data/bucket/symbol_bucket.js
@@ -132,6 +132,15 @@ class SymbolBuffers {
         this.placedSymbolArray = new PlacedSymbolArray();
     }
 
+    releaseBuffer() {
+        const keys = Object.keys(this);
+        for (const key of keys) {
+            if (this[key] && this[key].releaseBuffer) {
+                this[key].releaseBuffer();
+            }
+        }
+    }
+
     upload(context: Context, dynamicIndexBuffer: boolean, upload?: boolean, update?: boolean) {
         if (upload) {
             this.layoutVertexBuffer = context.createVertexBuffer(this.layoutVertexArray, symbolLayoutAttributes.members);
@@ -183,6 +192,15 @@ class CollisionBuffers {
         this.collisionVertexArray = new CollisionVertexArray();
     }
 
+    releaseBuffer() {
+        const keys = Object.keys(this);
+        for (const key of keys) {
+            if (this[key] && this[key].releaseBuffer) {
+                this[key].releaseBuffer();
+            }
+        }
+    }
+
     upload(context: Context) {
         this.layoutVertexBuffer = context.createVertexBuffer(this.layoutVertexArray, this.layoutAttributes);
         this.indexBuffer = context.createIndexBuffer(this.indexArray);
diff --git a/src/source/worker_tile.js b/src/source/worker_tile.js
index e70e0a2b9f2..8831d73ad61 100644
--- a/src/source/worker_tile.js
+++ b/src/source/worker_tile.js
@@ -204,6 +204,14 @@ class WorkerTile {
                     iconMap: this.returnDependencies ? iconMap : null,
                     glyphPositions: this.returnDependencies ? glyphAtlas.positions : null
                 });
+                values(buckets).filter(b => b.isEmpty()).forEach(emptyBucket => {
+                    const bucketKeys = Object.keys(emptyBucket);
+                    for (const key of bucketKeys) {
+                        if (emptyBucket[key] && emptyBucket[key].releaseBuffer) {
+                            emptyBucket[key].releaseBuffer();
+                        }
+                    }
+                });
             }
         }
     }
diff --git a/src/util/struct_array.js b/src/util/struct_array.js
index 9bed2979a7d..53c6bf88448 100644
--- a/src/util/struct_array.js
+++ b/src/util/struct_array.js
@@ -48,6 +48,16 @@ class Struct {
 const DEFAULT_CAPACITY = 128;
 const RESIZE_MULTIPLIER = 5;
 
+let resizeCount = 0;
+let reuseCount = 0;
+let sliceCount = 0;
+let noSliceCount = 0;
+let sizeCounts = {};
+let bufferPool = {};
+
+let constructedTypes = {};
+let transferedTypes = {};
+
 export type StructArrayMember = {
     name: string,
     type: ViewType,
@@ -140,10 +150,25 @@ class StructArray {
      * Resize the array to discard unused capacity.
      */
     _trim() {
+        transferedTypes[this.constructor.name] = true;
         if (this.length !== this.capacity) {
+            const prevSize = this.capacity * this.bytesPerElement;
+            if (!bufferPool[prevSize]) {
+                bufferPool[prevSize] = [];
+            }
+            bufferPool[prevSize].push(this.arrayBuffer);
             this.capacity = this.length;
             this.arrayBuffer = this.arrayBuffer.slice(0, this.length * this.bytesPerElement);
+            sliceCount++;
+            if (sliceCount % 1000 === 0) {
+                console.log(`${sliceCount} slices on ${resizeCount} allocations and ${reuseCount} buffers reused from pool, with ${noSliceCount} not requiring slice.`);
+                // for (const size in sizeCounts) {
+                //     console.log(`${size} allocated ${sizeCounts[size]} times`);
+                // }
+            }
             this._refreshViews();
+        } else {
+            noSliceCount++;
         }
     }
 
@@ -173,8 +198,29 @@ class StructArray {
      */
     reserve(n: number) {
         if (n > this.capacity) {
-            this.capacity = Math.max(n, Math.floor(this.capacity * RESIZE_MULTIPLIER), DEFAULT_CAPACITY);
-            this.arrayBuffer = new ArrayBuffer(this.capacity * this.bytesPerElement);
+            constructedTypes[this.constructor.name] = true;
+            const prevSize = this.capacity * this.bytesPerElement;
+            const exponent = Math.max(0, Math.ceil(Math.log(n * this.bytesPerElement / DEFAULT_CAPACITY) / Math.log(RESIZE_MULTIPLIER)));
+            const newSize = DEFAULT_CAPACITY * Math.pow(RESIZE_MULTIPLIER, exponent);//Math.max(n, Math.floor(this.capacity * RESIZE_MULTIPLIER), DEFAULT_CAPACITY);
+            this.capacity = newSize / this.bytesPerElement;
+            if (!sizeCounts[newSize]) {
+                sizeCounts[newSize] = 0;
+            }
+            sizeCounts[newSize]++;
+            if (prevSize > 0) {
+                if (!bufferPool[prevSize]) {
+                    bufferPool[prevSize] = [];
+                }
+                bufferPool[prevSize].push(this.arrayBuffer);
+            }
+
+            if (bufferPool[newSize] && bufferPool[newSize].length > 0) {
+                reuseCount++;
+                this.arrayBuffer = bufferPool[newSize].pop();
+            } else {
+                resizeCount++;
+                this.arrayBuffer = new ArrayBuffer(this.capacity * this.bytesPerElement);
+            }
 
             const oldUint8Array = this.uint8;
             this._refreshViews();
@@ -182,6 +228,16 @@ class StructArray {
         }
     }
 
+    releaseBuffer() {
+        const prevSize = this.capacity * this.bytesPerElement;
+        if (prevSize > 0) {
+            if (!bufferPool[prevSize]) {
+                bufferPool[prevSize] = [];
+            }
+            bufferPool[prevSize].push(this.arrayBuffer);
+        }
+    }
+
     /**
      * Create TypedArray views for the current ArrayBuffer.
      */