Add Win32EventPort::allowApc() to allow people to enable APCs.

Fixes #435

c++/src/kj/async-win32-test.c++

@@ -137,6 +137,31 @@ KJ_TEST("Win32IocpEventPort timer") {
   KJ_EXPECT(port.getTimer().now() - start >= 10 * MILLISECONDS);
 }
 
+VOID CALLBACK testApcProc(ULONG_PTR dwParam) {
+  reinterpret_cast<kj::PromiseFulfiller<void>*>(dwParam)->fulfill();
+}
+
+KJ_TEST("Win32IocpEventPort APC") {
+  if (GetProcAddress(GetModuleHandle("ntdll.dll"), "wine_get_version") != nullptr) {
+    // TODO(cleanup): Periodically check if Wine supports this yet.
+    KJ_LOG(WARNING, "detected that we're running under wine and this test won't work; skipping");
+    return;
+  }
+
+  Win32IocpEventPort port;
+  EventLoop loop(port);
+  WaitScope waitScope(loop);
+
+  port.allowApc();
+
+  auto paf = kj::newPromiseAndFulfiller<void>();
+
+  KJ_WIN32(QueueUserAPC(&testApcProc, GetCurrentThread(),
+      reinterpret_cast<ULONG_PTR>(paf.fulfiller.get())));
+
+  paf.promise.wait(waitScope);
+}
+
 }  // namespace
 }  // namespace kj
 

c++/src/kj/async-win32.c++

@@ -30,6 +30,8 @@
 #include <atomic>
 #include <chrono>
 #include "refcount.h"
+#include <ntsecapi.h>  // NTSTATUS
+#include <ntstatus.h>  // STATUS_SUCCESS
 
 #undef ERROR  // dammit windows.h
 
@@ -184,14 +186,41 @@ void Win32IocpEventPort::wake() const {
 }
 
 void Win32IocpEventPort::waitIocp(DWORD timeoutMs) {
+  if (isAllowApc) {
+    ULONG countReceived = 0;
+    OVERLAPPED_ENTRY entry;
+    memset(&entry, 0, sizeof(entry));
+
+    if (GetQueuedCompletionStatusEx(iocp, &entry, 1, &countReceived, timeoutMs, TRUE)) {
+      KJ_ASSERT(countReceived == 1);
+
+      if (entry.lpOverlapped == nullptr) {
+        // wake() called in another thread, or APC queued.
+      } else {
+        DWORD error = ERROR_SUCCESS;
+        if (entry.lpOverlapped->Internal != STATUS_SUCCESS) {
+          error = LsaNtStatusToWinError(entry.lpOverlapped->Internal);
+        }
+        static_cast<IoPromiseAdapter*>(entry.lpOverlapped)
+            ->done(IoResult { error, entry.dwNumberOfBytesTransferred });
+      }
+    } else {
+      // Call failed.
+      DWORD error = GetLastError();
+      if (error == WAIT_TIMEOUT || error == WAIT_IO_COMPLETION) {
+        // WAIT_TIMEOUT = timed out (dunno why this isn't ERROR_TIMEOUT??)
+        // WAIT_IO_COMPLETION = APC queued
+        // Either way, nothing to do.
+        return;
+      } else {
+        KJ_FAIL_WIN32("GetQueuedCompletionStatusEx()", error, error, entry.lpOverlapped);
+      }
+    }
+  } else {
     DWORD bytesTransferred;
     ULONG_PTR completionKey;
     LPOVERLAPPED overlapped = nullptr;
 
-  // TODO(someday): Should we use GetQueuedCompletionStatusEx()? It would allow us to read multiple
-  //   events in one call and would let us wait in an alertable state, which would allow users to
-  //   use APCs. However, it currently isn't implemented on Wine (as of 1.9.22).
-
     BOOL success = GetQueuedCompletionStatus(
         iocp, &bytesTransferred, &completionKey, &overlapped, timeoutMs);
 
@@ -210,6 +239,7 @@ void Win32IocpEventPort::waitIocp(DWORD timeoutMs) {
       DWORD error = success ? ERROR_SUCCESS : GetLastError();
       static_cast<IoPromiseAdapter*>(overlapped)->done(IoResult { error, bytesTransferred });
     }
+  }
 }
 
 bool Win32IocpEventPort::receivedWake() {

c++/src/kj/async-win32.h

@@ -136,6 +136,18 @@ public:
   // Given a handle that supports waiting for it to become "signaled" via WaitForSingleObject(),
   // return an object that can wait for this state using the EventPort.
 
+  // ---------------------------------------------------------------------------
+  // APCs
+
+  virtual void allowApc() = 0;
+  // If this is ever called, the Win32EventPort will switch modes so that APCs can be scheduled
+  // on the thread, e.g. through the Win32 QueueUserAPC() call. In the future, this may be enabled
+  // by default. However, as of this writing, Wine does not support the necessary
+  // GetQueuedCompletionStatusEx() call, thus allowApc() breaks Wine support. (Tested on Wine
+  // 1.8.7.)
+  //
+  // If the event port implementation can't support APCs for some reason, this throws.
+
   // ---------------------------------------------------------------------------
   // time
 
@@ -191,6 +203,7 @@ public:
   Own<IoObserver> observeIo(HANDLE handle) override;
   Own<SignalObserver> observeSignalState(HANDLE handle) override;
   Timer& getTimer() override { return timerImpl; }
+  void allowApc() override { isAllowApc = true; }
 
 private:
   class IoPromiseAdapter;
@@ -202,6 +215,7 @@ private:
   Win32WaitObjectThreadPool waitThreads;
   TimerImpl timerImpl;
   mutable std::atomic<bool> sentWake {false};
+  bool isAllowApc = false;
 
   static TimePoint readClock();