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Ability to capture a V8 heap profile and a heap snapshot

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This commit is contained in:
Karl Seguin
2026-01-22 10:26:54 +08:00
parent 24b7035b1b
commit b4759ae261
5 changed files with 81 additions and 7 deletions
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55
src/browser/js/Context.zig
View File

@@ -50,6 +50,8 @@ entered: bool,
cpu_profiler: ?*v8.CpuProfiler = null,
heap_profiler: ?*v8.HeapProfiler = null,
// references Env.templates
templates: []*const v8.FunctionTemplate,
@@ -823,6 +825,10 @@ pub fn startCpuProfiler(self: *Context) void {
@compileError("CPU Profiling is only available in debug builds");
}
var ls: js.Local.Scope = undefined;
self.localScope(&ls);
defer ls.deinit();
std.debug.assert(self.cpu_profiler == null);
v8.v8__CpuProfiler__UseDetailedSourcePositionsForProfiling(self.isolate.handle);
@@ -833,8 +839,55 @@ pub fn startCpuProfiler(self: *Context) void {
}
pub fn stopCpuProfiler(self: *Context) ![]const u8 {
var ls: js.Local.Scope = undefined;
self.localScope(&ls);
defer ls.deinit();
const title = self.isolate.initStringHandle("v8_cpu_profile");
const handle = v8.v8__CpuProfiler__StopProfiling(self.cpu_profiler.?, title) orelse return error.NoProfiles;
const string_handle = v8.v8__CpuProfile__Serialize(handle, self.isolate.handle) orelse return error.NoProfile;
return self.jsStringToZig(string_handle, .{});
return ls.local.jsStringToZig(string_handle, .{});
}
pub fn startHeapProfiler(self: *Context) void {
if (comptime !IS_DEBUG) {
@compileError("Heap Profiling is only available in debug builds");
}
var ls: js.Local.Scope = undefined;
self.localScope(&ls);
defer ls.deinit();
std.debug.assert(self.heap_profiler == null);
const heap_profiler = v8.v8__HeapProfiler__Get(self.isolate.handle).?;
// Sample every 32KB, stack depth 32
v8.v8__HeapProfiler__StartSamplingHeapProfiler(heap_profiler, 32 * 1024, 32);
v8.v8__HeapProfiler__StartTrackingHeapObjects(heap_profiler, true);
self.heap_profiler = heap_profiler;
}
pub fn stopHeapProfiler(self: *Context) !struct{[]const u8, []const u8} {
var ls: js.Local.Scope = undefined;
self.localScope(&ls);
defer ls.deinit();
const allocating = blk: {
const profile = v8.v8__HeapProfiler__GetAllocationProfile(self.heap_profiler.?);
const string_handle = v8.v8__AllocationProfile__Serialize(profile, self.isolate.handle);
v8.v8__HeapProfiler__StopSamplingHeapProfiler(self.heap_profiler.?);
v8.v8__AllocationProfile__Delete(profile);
break :blk try ls.local.jsStringToZig(string_handle, .{});
};
const snapshot = blk: {
const snapshot = v8.v8__HeapProfiler__TakeHeapSnapshot(self.heap_profiler.?, null) orelse return error.NoProfiles;
const string_handle = v8.v8__HeapSnapshot__Serialize(snapshot, self.isolate.handle);
v8.v8__HeapProfiler__StopTrackingHeapObjects(self.heap_profiler.?);
v8.v8__HeapSnapshot__Delete(snapshot);
break :blk try ls.local.jsStringToZig(string_handle, .{});
};
return .{allocating, snapshot};
}

23
src/lightpanda.zig
View File

@@ -51,7 +51,7 @@ pub fn fetch(app: *App, url: [:0]const u8, opts: FetchOpts) !void {
// defer {
// if (page.js.stopCpuProfiler()) |profile| {
// std.fs.cwd().writeFile(.{
// .sub_path = "v8/profile.json",
// .sub_path = ".lp-cache/cpu_profile.json",
// .data = profile,
// }) catch |err| {
// log.err(.app, "profile write error", .{ .err = err });
@@ -61,6 +61,27 @@ pub fn fetch(app: *App, url: [:0]const u8, opts: FetchOpts) !void {
// }
// }
// // Comment this out to get a heap V8 heap profil
// page.js.startHeapProfiler();
// defer {
// if (page.js.stopHeapProfiler()) |profile| {
// std.fs.cwd().writeFile(.{
// .sub_path = ".lp-cache/allocating.heapprofile",
// .data = profile.@"0",
// }) catch |err| {
// log.err(.app, "allocating write error", .{ .err = err });
// };
// std.fs.cwd().writeFile(.{
// .sub_path = ".lp-cache/snapshot.heapsnapshot",
// .data = profile.@"1",
// }) catch |err| {
// log.err(.app, "heapsnapshot write error", .{ .err = err });
// };
// } else |err| {
// log.err(.app, "profile error", .{ .err = err });
// }
// }
_ = try page.navigate(url, .{
.reason = .address_bar,
.kind = .{ .push = null },