win, tty: improve SIGWINCH performance

Continuing improvement of SIGWINCH from PR #2308.

Running SetWinEventHook without filtering for the specific PIDs has
significant impact on the performance of the entire system. This PR
changes the way SIGWINCH is handled.

The SetWinEventHook callback now signals a separate thread,
uv__tty_console_resize_watcher_thread. This thread calls
uv__tty_console_signal_resize() which checks if the console was actually
resized. The uv__tty_console_resize_watcher_thread makes sure to not to
call the uv__tty_console_signal_resize function more than 30 times per
second.

The SetWinEventHook will not be installed, if the PID of the
conhost.exe process that owns the console window cannot be
determinated. This can happen when a 32bit libuv app is running on a
64bit Windows.

For such cases PR #1408 is partially reverted - when tty reads
WINDOW_BUFFER_SIZE_EVENT, it will also trigger a call to
uv__tty_console_signal_resize(). This will also help when the app is
running under console emulators. Documentation was also updated to
reflect that.

Refs: microsoft/terminal#1811
Refs: microsoft/terminal#410
Refs: #2308

PR-URL: #2381
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

docs/src/signal.rst

@@ -20,6 +20,15 @@ Reception of some signals is emulated:
   program is given approximately 10 seconds to perform cleanup. After that
   Windows will unconditionally terminate it.
 
+* SIGWINCH is raised whenever libuv detects that the console has been
+  resized. When a libuv app is running under a console emulator, or when a
+  32-bit libuv app is running on 64-bit system, SIGWINCH will be emulated. In
+  such cases SIGWINCH signals may not always be delivered in a timely manner.
+  For a writable :c:type:`uv_tty_t` handle libuv will only detect size changes
+  when the cursor is moved. When a readable :c:type:`uv_tty_t` handle is used,
+  resizing of the console buffer will be detected only if the handle is in raw
+  mode and is being read.
+
 * Watchers for other signals can be successfully created, but these signals
   are never received. These signals are: `SIGILL`, `SIGABRT`, `SIGFPE`, `SIGSEGV`,
   `SIGTERM` and `SIGKILL.`
@@ -28,6 +37,8 @@ Reception of some signals is emulated:
   not detected by libuv; these will not trigger a signal watcher.
 
 .. versionchanged:: 1.15.0 SIGWINCH support on Windows was improved.
+.. versionchanged:: 1.31.0 32-bit libuv SIGWINCH support on 64-bit Windows was
+                           rolled back to old implementation.
 
 Unix notes
 ----------

src/win/tty.c

@@ -120,6 +120,8 @@ static int uv_tty_virtual_width = -1;
 static HANDLE uv__tty_console_handle = INVALID_HANDLE_VALUE;
 static int uv__tty_console_height = -1;
 static int uv__tty_console_width = -1;
+static HANDLE uv__tty_console_resized = INVALID_HANDLE_VALUE;
+static uv_mutex_t uv__tty_console_resize_mutex;
 
 static DWORD WINAPI uv__tty_console_resize_message_loop_thread(void* param);
 static void CALLBACK uv__tty_console_resize_event(HWINEVENTHOOK hWinEventHook,
@@ -129,6 +131,8 @@ static void CALLBACK uv__tty_console_resize_event(HWINEVENTHOOK hWinEventHook,
                                                   LONG idChild,
                                                   DWORD dwEventThread,
                                                   DWORD dwmsEventTime);
+static DWORD WINAPI uv__tty_console_resize_watcher_thread(void* param);
+static void uv__tty_console_signal_resize(void);
 
 /* We use a semaphore rather than a mutex or critical section because in some
    cases (uv__cancel_read_console) we need take the lock in the main thread and
@@ -168,6 +172,7 @@ void uv_console_init(void) {
     QueueUserWorkItem(uv__tty_console_resize_message_loop_thread,
                       NULL,
                       WT_EXECUTELONGFUNCTION);
+    uv_mutex_init(&uv__tty_console_resize_mutex);
   }
 }
 
@@ -728,6 +733,12 @@ void uv_process_tty_read_raw_req(uv_loop_t* loop, uv_tty_t* handle,
       }
       records_left--;
 
+      /* We might be not subscribed to EVENT_CONSOLE_LAYOUT or we might be
+       * running under some TTY emulator that does not send those events. */
+      if (handle->tty.rd.last_input_record.EventType == WINDOW_BUFFER_SIZE_EVENT) {
+        uv__tty_console_signal_resize();
+      }
+
       /* Ignore other events that are not key events. */
       if (handle->tty.rd.last_input_record.EventType != KEY_EVENT) {
         continue;
@@ -2299,15 +2310,24 @@ static DWORD WINAPI uv__tty_console_resize_message_loop_thread(void* param) {
                                       sizeof(conhost_pid),
                                       NULL);
 
-  if (!NT_SUCCESS(status))
+  if (!NT_SUCCESS(status)) {
     /* We couldn't retrieve our console host process, probably because this
      * is a 32-bit process running on 64-bit Windows. Fall back to receiving
-     * console events from all processes. */
-    conhost_pid = 0;
+     * console events from the input stream only. */
+    return 0;
+  }
 
   /* Ensure the PID is a multiple of 4, which is required by SetWinEventHook */
   conhost_pid &= ~(ULONG_PTR)0x3;
 
+  uv__tty_console_resized = CreateEvent(NULL, TRUE, FALSE, NULL);
+  if (uv__tty_console_resized == NULL)
+    return 0;
+  if (QueueUserWorkItem(uv__tty_console_resize_watcher_thread,
+                        NULL,
+                        WT_EXECUTELONGFUNCTION) == 0)
+    return 0;
+
   if (!pSetWinEventHook(EVENT_CONSOLE_LAYOUT,
                         EVENT_CONSOLE_LAYOUT,
                         NULL,
@@ -2331,6 +2351,20 @@ static void CALLBACK uv__tty_console_resize_event(HWINEVENTHOOK hWinEventHook,
                                                   LONG idChild,
                                                   DWORD dwEventThread,
                                                   DWORD dwmsEventTime) {
+  SetEvent(uv__tty_console_resized);
+}
+
+static DWORD WINAPI uv__tty_console_resize_watcher_thread(void* param) {
+  for (;;) {
+    /* Make sure to not overwhelm the system with resize events */
+    Sleep(33);
+    WaitForSingleObject(uv__tty_console_resized, INFINITE);
+    uv__tty_console_signal_resize();
+    ResetEvent(uv__tty_console_resized);
+  }
+}
+
+static void uv__tty_console_signal_resize(void) {
   CONSOLE_SCREEN_BUFFER_INFO sb_info;
   int width, height;
 
@@ -2340,9 +2374,13 @@ static void CALLBACK uv__tty_console_resize_event(HWINEVENTHOOK hWinEventHook,
   width = sb_info.dwSize.X;
   height = sb_info.srWindow.Bottom - sb_info.srWindow.Top + 1;
 
+  uv_mutex_lock(&uv__tty_console_resize_mutex);
   if (width != uv__tty_console_width || height != uv__tty_console_height) {
     uv__tty_console_width = width;
     uv__tty_console_height = height;
+    uv_mutex_unlock(&uv__tty_console_resize_mutex);
     uv__signal_dispatch(SIGWINCH);
+  } else {
+    uv_mutex_unlock(&uv__tty_console_resize_mutex);
   }
 }