Introduce interprocess signaling on Windows

This change gets rsync working without any warning or errors. On Windows
we now create a bunch of C:\var\sig\x\y.pid shared memory files, so sigs
can be delivered between processes. WinMain() creates this file when the
process starts. If the program links signaling system calls then we make
a thread at startup too, which allows asynchronous delivery each quantum
and cancelation points can spot these signals potentially faster on wait

See #1240

libc/intrin/itoa16.c

@@ -0,0 +1,36 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8                               :vi │
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2024 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/fmt/internal.h"
+
+textwindows char16_t *__itoa16(char16_t p[21], uint64_t x) {
+  char t;
+  size_t a, b, i = 0;
+  do {
+    p[i++] = x % 10 + '0';
+    x = x / 10;
+  } while (x > 0);
+  if (i) {
+    for (a = 0, b = i - 1; a < b; ++a, --b) {
+      t = p[a];
+      p[a] = p[b];
+      p[b] = t;
+    }
+  }
+  return p + i;
+}

libc/intrin/sig.c

@@ -17,11 +17,25 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/sysv/consts/sig.h"
+#include "libc/atomic.h"
 #include "libc/calls/sig.internal.h"
 #include "libc/calls/struct/sigset.internal.h"
 #include "libc/dce.h"
+#include "libc/fmt/internal.h"
 #include "libc/intrin/atomic.h"
 #include "libc/intrin/weaken.h"
+#include "libc/limits.h"
+#include "libc/nt/createfile.h"
+#include "libc/nt/enum/accessmask.h"
+#include "libc/nt/enum/creationdisposition.h"
+#include "libc/nt/enum/fileflagandattributes.h"
+#include "libc/nt/enum/filemapflags.h"
+#include "libc/nt/enum/filemovemethod.h"
+#include "libc/nt/enum/filesharemode.h"
+#include "libc/nt/enum/pageflags.h"
+#include "libc/nt/files.h"
+#include "libc/nt/memory.h"
+#include "libc/nt/runtime.h"
 #include "libc/thread/tls.h"
 
 struct Signals __sig;
@@ -52,3 +66,65 @@ void __sig_unblock(sigset_t m) {
     sys_sigprocmask(SIG_SETMASK, &m, 0);
   }
 }
+
+#ifdef __x86_64__
+
+textwindows char16_t *__sig_process_path(char16_t *path, uint32_t pid) {
+  char16_t *p = path;
+  *p++ = 'C';
+  *p++ = ':';
+  *p++ = '\\';
+  *p++ = 'v';
+  *p++ = 'a';
+  *p++ = 'r';
+  *p = 0;
+  CreateDirectory(path, 0);
+  *p++ = '\\';
+  *p++ = 's';
+  *p++ = 'i';
+  *p++ = 'g';
+  *p = 0;
+  CreateDirectory(path, 0);
+  *p++ = '\\';
+  p = __itoa16(p, (pid & 0x000fff00) >> 8);
+  *p = 0;
+  CreateDirectory(path, 0);
+  *p++ = '\\';
+  p = __itoa16(p, pid);
+  *p++ = '.';
+  *p++ = 'p';
+  *p++ = 'i';
+  *p++ = 'd';
+  *p = 0;
+  return path;
+}
+
+textwindows static atomic_ulong *__sig_map_process_impl(int pid) {
+  char16_t path[128];
+  intptr_t hand = CreateFile(__sig_process_path(path, pid),
+                             kNtGenericRead | kNtGenericWrite,
+                             kNtFileShareRead | kNtFileShareWrite, 0,
+                             kNtOpenAlways, kNtFileAttributeNormal, 0);
+  if (hand == -1)
+    return 0;
+  SetFilePointer(hand, 8, 0, kNtFileBegin);
+  SetEndOfFile(hand);
+  intptr_t map = CreateFileMapping(hand, 0, kNtPageReadwrite, 0, 8, 0);
+  if (!map) {
+    CloseHandle(hand);
+    return 0;
+  }
+  atomic_ulong *sigs = MapViewOfFileEx(map, kNtFileMapWrite, 0, 0, 8, 0);
+  CloseHandle(map);
+  CloseHandle(hand);
+  return sigs;
+}
+
+textwindows atomic_ulong *__sig_map_process(int pid) {
+  int e = errno;
+  atomic_ulong *res = __sig_map_process_impl(pid);
+  errno = e;
+  return res;
+}
+
+#endif /* __x86_64__ */

libc/intrin/sigprocmask-nt.c

@@ -17,6 +17,7 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/assert.h"
+#include "libc/atomic.h"
 #include "libc/calls/sig.internal.h"
 #include "libc/calls/struct/sigset.h"
 #include "libc/intrin/atomic.h"
@@ -34,7 +35,7 @@ textwindows int __sig_mask(int how, const sigset_t *neu, sigset_t *old) {
   }
 
   // get address of sigset to modify
-  _Atomic(uint64_t) *mask = &__get_tls()->tib_sigmask;
+  atomic_ulong *mask = &__get_tls()->tib_sigmask;
 
   // handle read-only case
   sigset_t oldmask;

libc/intrin/terminatethisprocess.c

@@ -16,8 +16,16 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/atomic.h"
+#include "libc/calls/sig.internal.h"
+#include "libc/intrin/kprintf.h"
+#include "libc/limits.h"
+#include "libc/nt/files.h"
+#include "libc/nt/memory.h"
 #include "libc/nt/runtime.h"
 #include "libc/nt/thunk/msabi.h"
+#include "libc/runtime/internal.h"
+#ifdef __x86_64__
 
 __msabi extern typeof(TerminateProcess) *const __imp_TerminateProcess;
 
@@ -25,8 +33,20 @@ __msabi extern typeof(TerminateProcess) *const __imp_TerminateProcess;
  * Terminates the calling process and all of its threads.
  */
 textwindows dontinstrument void TerminateThisProcess(uint32_t dwWaitStatus) {
+
+  // delete sig file
+  char16_t path[128];
+  atomic_ulong *real;
+  atomic_ulong fake = 0;
+  real = __sig.process;
+  __sig.process = &fake;
+  UnmapViewOfFile(real);
+  DeleteFile(__sig_process_path(path, __pid));
+
   // "When a process terminates itself, TerminateProcess stops execution
   // of the calling thread and does not return." -Quoth MSDN
   __imp_TerminateProcess(-1, dwWaitStatus);
   __builtin_unreachable();
 }
+
+#endif /* __x86_64__ */