Merge pull request #67 from mitchellh/wasm-shared

wasm: use shared, imported memory

build.zig

@@ -112,16 +112,44 @@ pub fn build(b: *std.build.Builder) !void {
 
     // wasm
     {
+        // Build our Wasm target.
+        const wasm_target: std.zig.CrossTarget = .{
+            .cpu_arch = .wasm32,
+            .os_tag = .freestanding,
+            .cpu_model = .{ .explicit = &std.Target.wasm.cpu.mvp },
+            .cpu_features_add = std.Target.wasm.featureSet(&.{
+                // We use this to explicitly request shared memory.
+                .atomics,
+
+                // Not explicitly used but compiler could use them if they want.
+                .bulk_memory,
+                .reference_types,
+                .sign_ext,
+            }),
+        };
+
+        // Whether we're using wasm shared memory. Some behaviors change.
+        // For now we require this but I wanted to make the code handle both
+        // up front.
+        const wasm_shared: bool = true;
+        exe_options.addOption(bool, "wasm_shared", wasm_shared);
+
         const wasm = b.addSharedLibrary(
             "ghostty-wasm",
             "src/main_wasm.zig",
             .{ .unversioned = {} },
         );
-        wasm.setTarget(.{ .cpu_arch = .wasm32, .os_tag = .freestanding });
+        wasm.setTarget(wasm_target);
         wasm.setBuildMode(mode);
         wasm.setOutputDir("zig-out");
         wasm.addOptions("build_options", exe_options);
 
+        // So that we can use web workers with our wasm binary
+        wasm.import_memory = true;
+        wasm.initial_memory = 65536 * 25;
+        wasm.max_memory = 65536 * 65536; // Maximum number of pages in wasm32
+        wasm.shared_memory = wasm_shared;
+
         // Stack protector adds extern requirements that we don't satisfy.
         wasm.stack_protector = false;
 
@@ -136,7 +164,7 @@ pub fn build(b: *std.build.Builder) !void {
         // it lets us test some basic functionality.
         const test_step = b.step("test-wasm", "Run all tests for wasm");
         const main_test = b.addTest("src/main_wasm.zig");
-        main_test.setTarget(.{ .cpu_arch = .wasm32, .os_tag = .wasi });
+        main_test.setTarget(wasm_target);
         main_test.addOptions("build_options", exe_options);
         try addDeps(b, main_test, true);
         test_step.dependOn(&main_test.step);

example/app.ts

@@ -4,9 +4,11 @@ const zjs = new ZigJS();
 const importObject = {
   module: {},
   env: {
+    memory: new WebAssembly.Memory({ initial: 25, maximum: 65536, shared: true }),
     log: (ptr: number, len: number) => {
-      const view = new DataView(zjs.memory.buffer, ptr, Number(len));
-      const str = new TextDecoder('utf-8').decode(view);
+      const arr = new Uint8ClampedArray(zjs.memory.buffer, ptr, len);
+      const data = arr.slice();
+      const str = new TextDecoder('utf-8').decode(data);
       console.log(str);
     },
   },
@@ -20,8 +22,8 @@ fetch(url.href).then(response =>
 ).then(bytes =>
   WebAssembly.instantiate(bytes, importObject)
 ).then(results => {
+  const memory = importObject.env.memory;
   const {
-    memory,
     malloc,
     free,
     face_new,

src/font/Atlas.zig

@@ -423,9 +423,17 @@ pub const Wasm = struct {
             defer mem_buf.deinit();
 
             // Create an array that points to our buffer
-            const Uint8ClampedArray = try js.global.get(js.Object, "Uint8ClampedArray");
-            defer Uint8ClampedArray.deinit();
-            const arr = try Uint8ClampedArray.new(.{ mem_buf, buf.ptr, buf.len });
+            const arr = arr: {
+                const Uint8ClampedArray = try js.global.get(js.Object, "Uint8ClampedArray");
+                defer Uint8ClampedArray.deinit();
+                const arr = try Uint8ClampedArray.new(.{ mem_buf, buf.ptr, buf.len });
+                if (!wasm.shared_mem) break :arr arr;
+
+                // If we're sharing memory then we have to copy the data since
+                // we can't set ImageData directly using a SharedArrayBuffer.
+                defer arr.deinit();
+                break :arr try arr.call(js.Object, "slice", .{});
+            };
             defer arr.deinit();
 
             // Create the image data from our array

src/os/wasm.zig

@@ -1,6 +1,7 @@
 //! This file contains helpers for wasm compilation.
 const std = @import("std");
 const builtin = @import("builtin");
+const options = @import("build_options");
 
 comptime {
     if (!builtin.target.isWasm()) {
@@ -8,6 +9,10 @@ comptime {
     }
 }
 
+/// True if we're in shared memory mode. If true, then the memory buffer
+/// in JS will be backed by a SharedArrayBuffer and some behaviors change.
+pub const shared_mem = options.wasm_shared;
+
 /// The allocator to use in wasm environments.
 ///
 /// The return values of this should NOT be sent to the host environment

vendor/zig-js

@@ -1 +1 @@
-Subproject commit 5e3a5ce776f7b424022494a830f66ace224fe7ff
+Subproject commit c89c1965cc6bf6ede97c1b891b624ce5282853d1