Write more tests for signal handling

There's now a much stronger level of assurance that signaling on Windows
will be atomic, low-latency, low tail latency, and shall never deadlock.

libc/calls/park.c

@@ -17,9 +17,17 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/internal.h"
+#include "libc/calls/sig.internal.h"
 #include "libc/calls/struct/sigset.h"
+#include "libc/calls/syscall_support-nt.internal.h"
 #include "libc/intrin/atomic.h"
+#include "libc/intrin/weaken.h"
+#include "libc/nt/enum/wait.h"
+#include "libc/nt/events.h"
+#include "libc/nt/runtime.h"
 #include "libc/nt/synchronization.h"
+#include "libc/sysv/consts/sicode.h"
+#include "libc/sysv/errfuns.h"
 #include "libc/thread/posixthread.internal.h"
 #ifdef __x86_64__
 
@@ -28,17 +36,39 @@
 // raises ECANCELED if this POSIX thread was canceled in masked mode
 textwindows static int _park_thread(uint32_t msdelay, sigset_t waitmask,
                                     bool restartable) {
-  if (__sigcheck(waitmask, restartable) == -1)
-    return -1;
-  int expect = 0;
-  atomic_int futex = 0;
   struct PosixThread *pt = _pthread_self();
+
+  // perform the wait operation
+  intptr_t sigev;
+  if (!(sigev = CreateEvent(0, 0, 0, 0)))
+    return __winerr();
+  pt->pt_event = sigev;
   pt->pt_blkmask = waitmask;
-  atomic_store_explicit(&pt->pt_blocker, &futex, memory_order_release);
-  bool32 ok = WaitOnAddress(&futex, &expect, sizeof(int), msdelay);
+  atomic_store_explicit(&pt->pt_blocker, PT_BLOCKER_EVENT,
+                        memory_order_release);
+  //!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!//
+  int sig = 0;
+  uint32_t ws = 0;
+  if (!_is_canceled() &&
+      !(_weaken(__sig_get) && (sig = _weaken(__sig_get)(waitmask))))
+    ws = WaitForSingleObject(sigev, msdelay);
+  //!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!//
   atomic_store_explicit(&pt->pt_blocker, 0, memory_order_release);
-  if (ok && __sigcheck(waitmask, restartable) == -1)
+  CloseHandle(sigev);
+
+  // recursion is now safe
+  if (ws == -1)
+    return __winerr();
+  int handler_was_called = 0;
+  if (sig)
+    handler_was_called = _weaken(__sig_relay)(sig, SI_KERNEL, waitmask);
+  if (_check_cancel())
     return -1;
+  if (handler_was_called & SIG_HANDLED_NO_RESTART)
+    return eintr();
+  if (handler_was_called & SIG_HANDLED_SA_RESTART)
+    if (!restartable)
+      return eintr();
   return 0;
 }