Add Update and Signpost support

Sources/OpenSwiftUI/Core/Log/Signpost.swift

@@ -0,0 +1,42 @@
+//
+//  Signpost.swift
+//  OpenSwiftUI
+//
+//  Audited for RELEASE_2021
+//  Status: WIP
+//  ID: 34756F646CF7AC3DBE2A8E0B344C962F
+
+import os.signpost
+
+struct Signpost {
+    private let style: Style
+    private let stability: Stability
+
+    // TODO
+    var isEnabled: Bool {
+        switch stability {
+        case .disabled, .verbose, .debug:
+            return false
+        case .published:
+            return true
+        }
+    }
+
+    static let viewHost = Signpost(style: .kdebug(0), stability: .published)
+}
+
+extension Signpost {
+    private enum Style {
+        case kdebug(UInt8)
+        case os_log(StaticString)
+    }
+
+    private enum Stability: Hashable {
+        case disabled
+        case verbose
+        case debug
+        case published
+    }
+}
+
+

Sources/OpenSwiftUI/Core/Update/Update.swift

@@ -0,0 +1,83 @@
+//
+//  Update.swift
+//  OpenSwiftUI
+//
+//  Status: WIP
+//  ID: EA173074DA35FA471DC70643259B7E74
+
+internal import COpenSwiftUI
+internal import OpenGraphShims
+
+extension MovableLock {
+    @inline(__always)
+    func withLock<R>(_ body: () -> R) -> R {
+        lock()
+        defer { unlock() }
+        return body()
+    }
+}
+
+enum Update {
+    static let trackHost: AnyObject = TraceHost()
+    private static let lock = MovableLock.create()
+    private static var depth = 0
+    private static var actions: [() -> Void] = []
+
+    static func begin() {
+        lock.lock()
+        depth += 1
+        if depth == 1 {
+            guard Signpost.viewHost.isEnabled else {
+                return
+            }
+            // TODO: Signpost
+        }
+    }
+
+    static func end() {
+        if depth == 1 {
+            dispatchActions()
+            // TODO: Signpost
+        }
+        depth -= 1
+        lock.unlock()
+    }
+
+    static func enqueueAction(_ action: @escaping () -> Void) {
+        begin()
+        actions.append(action)
+        end()
+    }
+
+    static func ensure<Value>(_ body: () -> Value) throws -> Value {
+        lock.withLock {
+            if depth == 0 {
+                begin()
+            }
+            defer {
+                if depth == 0 {
+                    end()
+                }
+            }
+            return body()
+        }
+    }
+
+    @inlinable
+    static func dispatchActions() {
+        // FIXME
+        for action in actions {
+            action()
+        }
+    }
+
+    @inlinable
+    static func syncMain(_ body: () -> Void) {
+        // TODO
+        fatalError("TODO")
+    }
+}
+
+extension Update {
+    private class TraceHost {}
+}