Implement signal handler tail recursion

GNU Make on Windows now appears to be working reliably. This change also
fixes a bug where, after fork the Windows thread handle wasn't reset and
that caused undefined behavior using SetThreadContext() with our signals

test/libc/proc/handkill_test.c

@@ -0,0 +1,151 @@
+/*-*- 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 2023 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/atomic.h"
+#include "libc/calls/calls.h"
+#include "libc/calls/struct/sigaction.h"
+#include "libc/calls/struct/sigset.h"
+#include "libc/dce.h"
+#include "libc/nt/process.h"
+#include "libc/nt/thread.h"
+#include "libc/runtime/clktck.h"
+#include "libc/runtime/runtime.h"
+#include "libc/str/str.h"
+#include "libc/sysv/consts/sig.h"
+#include "libc/testlib/subprocess.h"
+#include "libc/testlib/testlib.h"
+#include "libc/thread/posixthread.internal.h"
+#include "libc/thread/thread.h"
+
+// test we can:
+// 1. raise the same signal inside the signal handler
+// 2. that the signal will trigger immediately after handling
+
+struct SharedMemory {
+  pthread_t target;
+  atomic_bool ready;
+  atomic_bool got_signal;
+  atomic_bool handler_returned;
+} * shm;
+
+void OnSig(int sig) {
+  signal(SIGUSR1, SIG_DFL);
+  raise(SIGUSR1);
+  shm->got_signal = true;
+}
+
+void SetUpOnce(void) {
+  signal(SIGUSR1, OnSig);
+  shm = _mapshared(sizeof(*shm));
+}
+
+void TearDownOnce(void) {
+  munmap(shm, sizeof(*shm));
+}
+
+void SetUp(void) {
+  bzero(shm, sizeof(*shm));
+}
+
+void *Killer(void *arg) {
+  ASSERT_EQ(0, pthread_kill(shm->target, SIGUSR1));
+  return 0;
+}
+
+void *Killed(void *arg) {
+  shm->ready = true;
+  while (!shm->got_signal) donothing;
+  shm->handler_returned = true;
+  return 0;
+}
+
+TEST(handkill, raise) {
+  SPAWN(fork);
+  raise(SIGUSR1);
+  shm->handler_returned = true;
+  TERMS(SIGUSR1);
+  EXPECT_TRUE(shm->got_signal);
+  EXPECT_FALSE(shm->handler_returned);
+}
+
+TEST(handkill, main2thread_async) {
+  SPAWN(fork);
+  pthread_t th;
+  shm->target = pthread_self();
+  pthread_create(&th, 0, Killed, 0);
+  while (!shm->ready) donothing;
+  ASSERT_EQ(0, pthread_kill(th, SIGUSR1));
+  ASSERT_EQ(0, pthread_join(th, 0));
+  TERMS(SIGUSR1);
+  EXPECT_TRUE(shm->got_signal);
+  EXPECT_FALSE(shm->handler_returned);
+}
+
+TEST(handkill, thread2main_async) {
+  SPAWN(fork);
+  pthread_t th;
+  shm->target = pthread_self();
+  pthread_create(&th, 0, Killer, 0);
+  while (!shm->got_signal) donothing;
+  shm->handler_returned = true;
+  pthread_join(th, 0);
+  TERMS(SIGUSR1);
+  EXPECT_TRUE(shm->got_signal);
+  EXPECT_FALSE(shm->handler_returned);
+}
+
+TEST(handkill, thread2thread_async) {
+  SPAWN(fork);
+  pthread_t th;
+  pthread_create(&shm->target, 0, Killed, 0);
+  pthread_create(&th, 0, Killer, 0);
+  pthread_join(shm->target, 0);
+  pthread_join(th, 0);
+  TERMS(SIGUSR1);
+  EXPECT_TRUE(shm->got_signal);
+  EXPECT_FALSE(shm->handler_returned);
+}
+
+TEST(handkill, process_async) {
+  if (IsWindows()) return;
+  SPAWN(fork);
+  shm->ready = true;
+  while (!shm->got_signal) donothing;
+  shm->handler_returned = true;
+  PARENT();
+  while (!shm->ready) donothing;
+  ASSERT_SYS(0, 0, kill(child, SIGUSR1));
+  WAIT(term, SIGUSR1);
+  EXPECT_TRUE(shm->got_signal);
+  EXPECT_FALSE(shm->handler_returned);
+}
+
+TEST(handkill, process_pause) {
+  if (IsWindows()) return;
+  SPAWN(fork);
+  shm->ready = true;
+  pause();
+  shm->handler_returned = true;
+  PARENT();
+  while (!shm->ready) donothing;
+  usleep(1e6 / CLK_TCK * 2);
+  ASSERT_SYS(0, 0, kill(child, SIGUSR1));
+  WAIT(term, SIGUSR1);
+  EXPECT_TRUE(shm->got_signal);
+  EXPECT_FALSE(shm->handler_returned);
+}