Overhaul Windows signal handling

The new asynchronous signal delivery technique is now also being used
for tkill(), raise(), etc. Many subtle issues have been addresesd. We
now signal handling on Windows that's remarkably similar to the POSIX
behaviors. However that's just across threads. We're lacking a way to
have the signal semantics work well, across multiple WIN32 processes.

libc/calls/tkill.c

@@ -0,0 +1,128 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
+#include "libc/calls/calls.h"
+#include "libc/calls/sig.internal.h"
+#include "libc/calls/state.internal.h"
+#include "libc/calls/syscall-sysv.internal.h"
+#include "libc/calls/syscall_support-nt.internal.h"
+#include "libc/dce.h"
+#include "libc/errno.h"
+#include "libc/intrin/atomic.h"
+#include "libc/intrin/dll.h"
+#include "libc/intrin/strace.internal.h"
+#include "libc/nt/enum/context.h"
+#include "libc/nt/enum/threadaccess.h"
+#include "libc/nt/runtime.h"
+#include "libc/nt/struct/context.h"
+#include "libc/nt/thread.h"
+#include "libc/sysv/consts/sicode.h"
+#include "libc/sysv/consts/sig.h"
+#include "libc/sysv/errfuns.h"
+#include "libc/thread/posixthread.internal.h"
+#include "libc/thread/thread.h"
+#include "libc/thread/tls.h"
+
+static dontinline textwindows int __tkill_nt(int tid, int sig,
+                                             struct CosmoTib *tib) {
+
+  // validate api usage
+  if (tid <= 0 || !(1 <= sig && sig <= 64)) {
+    return einval();
+  }
+
+  // check if caller is killing themself
+  if (tid == gettid() && __tls_enabled && (!tib || tib == __get_tls())) {
+    struct NtContext nc = {.ContextFlags = kNtContextAll};
+    struct Delivery pkg = {0, sig, SI_TKILL, &nc};
+    unassert(GetThreadContext(GetCurrentThread(), &nc));
+    __sig_tramp(&pkg);
+    return 0;
+  }
+
+  // check to see if this is a cosmo posix thread
+  struct Dll *e;
+  pthread_spin_lock(&_pthread_lock);
+  for (e = dll_first(_pthread_list); e; e = dll_next(_pthread_list, e)) {
+    enum PosixThreadStatus status;
+    struct PosixThread *pt = POSIXTHREAD_CONTAINER(e);
+    int rhs = atomic_load_explicit(&pt->tib->tib_tid, memory_order_acquire);
+    if (rhs <= 0 || tid != rhs) continue;
+    if (tib && tib != pt->tib) continue;
+    status = atomic_load_explicit(&pt->status, memory_order_acquire);
+    pthread_spin_unlock(&_pthread_lock);
+    if (status < kPosixThreadTerminated) {
+      if (pt->flags & PT_BLOCKED) {
+        return __sig_add(tid, sig, SI_TKILL);
+      } else {
+        return _pthread_signal(pt, sig, SI_TKILL);
+      }
+    } else {
+      return 0;
+    }
+  }
+  pthread_spin_unlock(&_pthread_lock);
+
+  // otherwise try our luck hunting a win32 thread
+  if (!tib) {
+    intptr_t h;
+    if ((h = OpenThread(kNtThreadTerminate, false, tid))) {
+      if (TerminateThread(h, sig)) {
+        return 0;
+      } else {
+        return __winerr();
+      }
+      CloseHandle(h);
+    } else {
+      return __winerr();
+    }
+  } else {
+    return esrch();
+  }
+}
+
+// OpenBSD has an optional `tib` parameter for extra safety.
+int __tkill(int tid, int sig, void *tib) {
+  int rc;
+  if (IsLinux() || IsXnu() || IsFreebsd() || IsOpenbsd() || IsNetbsd()) {
+    rc = sys_tkill(tid, sig, tib);
+  } else if (IsWindows()) {
+    rc = __tkill_nt(tid, sig, tib);
+  } else {
+    rc = enosys();
+  }
+  STRACE("tkill(%d, %G) → %d% m", tid, sig, rc);
+  return rc;
+}
+
+/**
+ * Kills thread.
+ *
+ * @param tid is thread id
+ * @param sig does nothing on xnu
+ * @return 0 on success, or -1 w/ errno
+ * @raise EAGAIN if `RLIMIT_SIGPENDING` was exceeded
+ * @raise EINVAL if `tid` or `sig` were invalid
+ * @raise ESRCH if no such `tid` existed
+ * @raise EPERM if permission was denied
+ * @asyncsignalsafe
+ */
+int tkill(int tid, int sig) {
+  return __tkill(tid, sig, 0);
+}