From 9d372f48dd263c20138828842ff8655d694f7e61 Mon Sep 17 00:00:00 2001
From: Justine Tunney <jtunney@gmail.com>
Date: Mon, 9 Oct 2023 20:18:48 -0700
Subject: [PATCH] Fix some issues

---
 ape/ape-m1.c                                  | 53 +++++++++++++++-
 ape/loader.c                                  |  1 +
 libc/calls/assertfail.c                       |  2 +-
 libc/calls/clock_nanosleep-xnu.c              |  4 +-
 libc/calls/clock_nanosleep.c                  | 17 +++++-
 libc/calls/sigaction.c                        | 20 +++++-
 libc/calls/sigaltstack.c                      | 11 +++-
 libc/calls/sigenter-xnu.c                     | 16 ++---
 libc/calls/sleep.c                            | 25 ++++++--
 libc/calls/struct/sigaction.internal.h        |  7 +++
 libc/calls/timespec_sleep.c                   | 23 +++++--
 libc/calls/timespec_sleep_until.c             |  2 +-
 libc/calls/usleep.c                           |  5 +-
 libc/log/appendresourcereport.c               |  3 +
 libc/proc/execve-nt.greg.c                    |  5 +-
 libc/runtime/syslib.internal.h                |  9 +++
 libc/stdio/printargs.c                        |  2 +
 libc/thread/pthread_cancel.c                  | 13 ++--
 libc/thread/sem_open.c                        | 42 +++++++++++--
 libc/thread/sem_post.c                        | 10 +++
 libc/thread/sem_timedwait.c                   | 48 ++++++++++++++-
 libc/thread/sem_trywait.c                     | 10 +++
 libc/thread/semaphore.h                       |  2 +
 test/libc/thread/pthread_cancel_test.c        | 27 ++++++++
 test/libc/thread/pthread_kill_test.c          |  3 -
 .../Modules/_multiprocessing/semaphore.c      |  2 +-
 tool/build/runit.c                            |  7 ---
 tool/viz/clock_nanosleep_accuracy.c           |  6 --
 tool/viz/setitimer_accuracy.c                 | 61 +++++++++++++++++++
 29 files changed, 373 insertions(+), 63 deletions(-)
 create mode 100644 tool/viz/setitimer_accuracy.c

diff --git a/ape/ape-m1.c b/ape/ape-m1.c
index d77cefd5161..9fdcc885e88 100644
--- a/ape/ape-m1.c
+++ b/ape/ape-m1.c
@@ -30,10 +30,11 @@
 #include <sys/uio.h>
 #include <time.h>
 #include <unistd.h>
+#include <semaphore.h>
 
 #define pagesz         16384
 #define SYSLIB_MAGIC   ('s' | 'l' << 8 | 'i' << 16 | 'b' << 24)
-#define SYSLIB_VERSION 4
+#define SYSLIB_VERSION 5
 
 struct Syslib {
   int magic;
@@ -79,6 +80,15 @@ struct Syslib {
   long (*pselect)(int, fd_set *, fd_set *, fd_set *, const struct timespec *,
                   const sigset_t *);
   long (*mprotect)(void *, size_t, int);
+  /* v5 (2023-10-09) */
+  long (*sigaltstack)(const stack_t *, stack_t *);
+  long (*getentropy)(void *, size_t);
+  long (*sem_open)(const char *, int, uint16_t, unsigned);
+  long (*sem_unlink)(const char *);
+  long (*sem_close)(int *);
+  long (*sem_post)(int *);
+  long (*sem_wait)(int *);
+  long (*sem_trywait)(int *);
 };
 
 #define ELFCLASS32  1
@@ -350,6 +360,7 @@ static char AccessCommand(struct PathSearcher *ps, unsigned long pathlen) {
   if (pathlen + 1 + ps->namelen + 1 > sizeof(ps->path)) return 0;
   if (pathlen && ps->path[pathlen - 1] != '/') ps->path[pathlen++] = '/';
   MemMove(ps->path + pathlen, ps->name, ps->namelen);
+  ps->path[pathlen + ps->namelen] = 0;
   return !access(ps->path, X_OK);
 }
 
@@ -795,6 +806,38 @@ static long sys_mprotect(void *data, size_t size, int prot) {
   return sysret(mprotect(data, size, prot));
 }
 
+static long sys_sigaltstack(const stack_t *ss, stack_t *oss) {
+  return sysret(sigaltstack(ss, oss));
+}
+
+static long sys_getentropy(void *buf, size_t buflen) {
+  return sysret(getentropy(buf, buflen));
+}
+
+static long sys_sem_open(const char *name, int oflags, mode_t mode, unsigned value) {
+  return sysret((long)sem_open(name, oflags, mode, value));
+}
+
+static long sys_sem_unlink(const char *name) {
+  return sysret(sem_unlink(name));
+}
+
+static long sys_sem_close(sem_t *sem) {
+  return sysret(sem_close(sem));
+}
+
+static long sys_sem_post(sem_t *sem) {
+  return sysret(sem_post(sem));
+}
+
+static long sys_sem_wait(sem_t *sem) {
+  return sysret(sem_wait(sem));
+}
+
+static long sys_sem_trywait(sem_t *sem) {
+  return sysret(sem_trywait(sem));
+}
+
 static long sys_write(int fd, const void *data, size_t size) {
   return sysret(write(fd, data, size));
 }
@@ -879,6 +922,14 @@ int main(int argc, char **argv, char **envp) {
   M->lib.sigaction = sys_sigaction;
   M->lib.pselect = sys_pselect;
   M->lib.mprotect = sys_mprotect;
+  M->lib.sigaltstack = sys_sigaltstack;
+  M->lib.getentropy = sys_getentropy;
+  M->lib.sem_open = sys_sem_open;
+  M->lib.sem_unlink = sys_sem_unlink;
+  M->lib.sem_close = sys_sem_close;
+  M->lib.sem_post = sys_sem_post;
+  M->lib.sem_wait = sys_sem_wait;
+  M->lib.sem_trywait = sys_sem_trywait;
 
   /* getenv("_") is close enough to at_execfn */
   execfn = argc > 0 ? argv[0] : 0;
diff --git a/ape/loader.c b/ape/loader.c
index 74b2cf6f443..67b96f9a3b9 100644
--- a/ape/loader.c
+++ b/ape/loader.c
@@ -538,6 +538,7 @@ static char AccessCommand(struct PathSearcher *ps, unsigned long pathlen) {
   if (pathlen + 1 + ps->namelen + 1 > sizeof(ps->path)) return 0;
   if (pathlen && ps->path[pathlen - 1] != '/') ps->path[pathlen++] = '/';
   MemMove(ps->path + pathlen, ps->name, ps->namelen);
+  ps->path[pathlen + ps->namelen] = 0;
   return !Access(ps->path, X_OK, ps->os);
 }
 
diff --git a/libc/calls/assertfail.c b/libc/calls/assertfail.c
index a8fe202ee46..5399980864d 100644
--- a/libc/calls/assertfail.c
+++ b/libc/calls/assertfail.c
@@ -29,7 +29,7 @@
 void __assert_fail(const char *expr, const char *file, int line) {
   char ibuf[12];
   FormatInt32(ibuf, line);
-  tinyprint(2, "\n", file, ":", ibuf, ": assert(", expr, ") failed (",
+  tinyprint(2, file, ":", ibuf, ": assert(", expr, ") failed (",
             program_invocation_short_name, " ",
             DescribeBacktrace(__builtin_frame_address(0)), ")\n", NULL);
   abort();
diff --git a/libc/calls/clock_nanosleep-xnu.c b/libc/calls/clock_nanosleep-xnu.c
index f0502ac007a..e8ad33c800e 100644
--- a/libc/calls/clock_nanosleep-xnu.c
+++ b/libc/calls/clock_nanosleep-xnu.c
@@ -16,6 +16,7 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
 #include "libc/calls/struct/timespec.h"
 #include "libc/calls/struct/timespec.internal.h"
 #include "libc/calls/struct/timeval.h"
@@ -27,6 +28,7 @@
 #include "libc/sysv/consts/clock.h"
 #include "libc/sysv/consts/timer.h"
 #include "libc/sysv/errfuns.h"
+#include "libc/thread/posixthread.internal.h"
 #include "libc/thread/thread.h"
 
 int sys_clock_nanosleep_xnu(int clock, int flags, const struct timespec *req,
@@ -74,7 +76,7 @@ int sys_clock_nanosleep_xnu(int clock, int flags, const struct timespec *req,
   }
   if (res == -EINTR &&                    //
       (_weaken(pthread_testcancel_np) &&  //
-       _weaken(pthread_testcancel_np))) {
+       _weaken(pthread_testcancel_np)())) {
     return ecanceled();
   }
   return _sysret(res);
diff --git a/libc/calls/clock_nanosleep.c b/libc/calls/clock_nanosleep.c
index ca69816c70d..3db418207f6 100644
--- a/libc/calls/clock_nanosleep.c
+++ b/libc/calls/clock_nanosleep.c
@@ -23,11 +23,14 @@
 #include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/intrin/describeflags.internal.h"
+#include "libc/intrin/kprintf.h"
 #include "libc/intrin/strace.internal.h"
+#include "libc/intrin/weaken.h"
 #include "libc/runtime/clktck.h"
 #include "libc/sysv/consts/clock.h"
 #include "libc/sysv/consts/timer.h"
 #include "libc/sysv/errfuns.h"
+#include "libc/thread/thread.h"
 
 static int sys_clock_nanosleep(int clock, int flags,  //
                                const struct timespec *req,
@@ -45,6 +48,16 @@ static int sys_clock_nanosleep(int clock, int flags,  //
   } else {
     rc = enosys();
   }
+  if (rc > 0) {
+    errno = rc;
+    rc = -1;
+  }
+  // system call support might not detect cancelation on bsds
+  if (rc == -1 && errno == EINTR &&      //
+      _weaken(pthread_testcancel_np) &&  //
+      _weaken(pthread_testcancel_np)()) {
+    rc = ecanceled();
+  }
   END_CANCELATION_POINT;
   STRACE("sys_clock_nanosleep(%s, %s, %s, [%s]) → %d% m",
          DescribeClockName(clock), DescribeSleepFlags(flags),
@@ -62,11 +75,11 @@ static int cosmo_clock_nanosleep(int clock, int flags,
   if (clock == CLOCK_REALTIME ||  //
       clock == CLOCK_REALTIME_PRECISE) {
     time_clock = clock;
-    sleep_clock = CLOCK_REALTIME_PRECISE;
+    sleep_clock = CLOCK_REALTIME;
   } else if (clock == CLOCK_MONOTONIC ||  //
              clock == CLOCK_MONOTONIC_PRECISE) {
     time_clock = clock;
-    sleep_clock = CLOCK_MONOTONIC_PRECISE;
+    sleep_clock = CLOCK_MONOTONIC;
   } else if (clock == CLOCK_REALTIME_COARSE ||  //
              clock == CLOCK_REALTIME_FAST) {
     return sys_clock_nanosleep(CLOCK_REALTIME, flags, req, rem);
diff --git a/libc/calls/sigaction.c b/libc/calls/sigaction.c
index e03791afc06..10d4df1c225 100644
--- a/libc/calls/sigaction.c
+++ b/libc/calls/sigaction.c
@@ -41,6 +41,7 @@
 #include "libc/macros.internal.h"
 #include "libc/mem/mem.h"
 #include "libc/runtime/runtime.h"
+#include "libc/runtime/syslib.internal.h"
 #include "libc/str/str.h"
 #include "libc/sysv/consts/limits.h"
 #include "libc/sysv/consts/sa.h"
@@ -70,6 +71,10 @@ static void sigaction_cosmo2native(union metasigaction *sa) {
     sa->linux.sa_restorer = restorer;
     sa->linux.sa_mask[0] = masklo;
     sa->linux.sa_mask[1] = maskhi;
+  } else if (IsXnuSilicon()) {
+    sa->silicon.sa_flags = flags;
+    sa->silicon.sa_handler = handler;
+    sa->silicon.sa_mask[0] = masklo;
   } else if (IsXnu()) {
     sa->xnu_in.sa_flags = flags;
     sa->xnu_in.sa_handler = handler;
@@ -109,6 +114,10 @@ static void sigaction_native2cosmo(union metasigaction *sa) {
     restorer = sa->linux.sa_restorer;
     masklo = sa->linux.sa_mask[0];
     maskhi = sa->linux.sa_mask[1];
+  } else if (IsXnu()) {
+    flags = sa->silicon.sa_flags;
+    handler = sa->silicon.sa_handler;
+    masklo = sa->silicon.sa_mask[0];
   } else if (IsXnu()) {
     flags = sa->xnu_out.sa_flags;
     handler = sa->xnu_out.sa_handler;
@@ -142,6 +151,7 @@ static int __sigaction(int sig, const struct sigaction *act,
       (sizeof(struct sigaction) >= sizeof(struct sigaction_linux) &&
        sizeof(struct sigaction) >= sizeof(struct sigaction_xnu_in) &&
        sizeof(struct sigaction) >= sizeof(struct sigaction_xnu_out) &&
+       sizeof(struct sigaction) >= sizeof(struct sigaction_silicon) &&
        sizeof(struct sigaction) >= sizeof(struct sigaction_freebsd) &&
        sizeof(struct sigaction) >= sizeof(struct sigaction_openbsd) &&
        sizeof(struct sigaction) >= sizeof(struct sigaction_netbsd)),
@@ -193,6 +203,9 @@ static int __sigaction(int sig, const struct sigaction *act,
         // mitigate Rosetta signal handling strangeness
         // https://github.com/jart/cosmopolitan/issues/455
         ap->sa_flags |= SA_SIGINFO;
+      } else if (IsXnu()) {
+        sigenter = __sigenter_xnu;
+        ap->sa_flags |= SA_SIGINFO;  // couldn't hurt
       } else if (IsNetbsd()) {
         sigenter = __sigenter_netbsd;
       } else if (IsFreebsd()) {
@@ -231,7 +244,12 @@ static int __sigaction(int sig, const struct sigaction *act,
       arg4 = 8; /* or linux whines */
       arg5 = 0;
     }
-    if ((rc = sys_sigaction(sig, ap, oldact, arg4, arg5)) != -1) {
+    if (!IsXnuSilicon()) {
+      rc = sys_sigaction(sig, ap, oldact, arg4, arg5);
+    } else {
+      rc = _sysret(__syslib->__sigaction(sig, ap, oldact));
+    }
+    if (rc != -1) {
       sigaction_native2cosmo((union metasigaction *)oldact);
     }
   } else {
diff --git a/libc/calls/sigaltstack.c b/libc/calls/sigaltstack.c
index 8afcb94ba76..69ea9bb84d5 100644
--- a/libc/calls/sigaltstack.c
+++ b/libc/calls/sigaltstack.c
@@ -25,6 +25,7 @@
 #include "libc/intrin/describeflags.internal.h"
 #include "libc/intrin/strace.internal.h"
 #include "libc/runtime/runtime.h"
+#include "libc/runtime/syslib.internal.h"
 #include "libc/sysv/consts/ss.h"
 #include "libc/sysv/errfuns.h"
 #include "libc/thread/tls.h"
@@ -82,9 +83,17 @@ static textwindows int sigaltstack_cosmo(const struct sigaltstack *neu,
 
 static int sigaltstack_bsd(const struct sigaltstack *neu,
                            struct sigaltstack *old) {
+  int rc;
   struct sigaltstack_bsd oldbsd, neubsd, *neup = 0;
   if (neu) sigaltstack2bsd(&neubsd, neu), neup = &neubsd;
-  if (sys_sigaltstack(neup, &oldbsd) == -1) return -1;
+  if (IsXnuSilicon()) {
+    rc = _sysret(__syslib->__sigaltstack(neup, &oldbsd));
+  } else {
+    rc = sys_sigaltstack(neup, &oldbsd);
+  }
+  if (rc == -1) {
+    return -1;
+  }
   if (old) sigaltstack2linux(old, &oldbsd);
   return 0;
 }
diff --git a/libc/calls/sigenter-xnu.c b/libc/calls/sigenter-xnu.c
index 741839ab41d..fb6628fed00 100644
--- a/libc/calls/sigenter-xnu.c
+++ b/libc/calls/sigenter-xnu.c
@@ -486,9 +486,14 @@ static privileged void linuxssefpustate2xnu(
 
 #endif /* __x86_64__ */
 
+#ifdef __x86_64__
 privileged void __sigenter_xnu(void *fn, int infostyle, int sig,
                                struct siginfo_xnu *xnuinfo,
                                struct __darwin_ucontext *xnuctx) {
+#else
+privileged void __sigenter_xnu(int sig, struct siginfo_xnu *xnuinfo,
+                               struct __darwin_ucontext *xnuctx) {
+#endif
 #pragma GCC push_options
 #pragma GCC diagnostic ignored "-Wframe-larger-than="
   struct Goodies {
@@ -579,15 +584,6 @@ privileged void __sigenter_xnu(void *fn, int infostyle, int sig,
                : "=a"(ax)
                : "0"(0x20000b8 /* sigreturn */), "D"(xnuctx), "S"(infostyle)
                : "rcx", "r11", "memory", "cc");
-#else
-  register long r0 asm("x0") = (long)xnuctx;
-  register long r1 asm("x1") = (long)infostyle;
-  asm volatile("mov\tx16,%0\n\t"
-               "svc\t0"
-               : /* no outputs */
-               : "i"(0x0b8 /* sigreturn */), "r"(r0), "r"(r1)
-               : "x16", "memory");
-#endif /* __x86_64__ */
-
   notpossible;
+#endif /* __x86_64__ */
 }
diff --git a/libc/calls/sleep.c b/libc/calls/sleep.c
index 639b74380cc..18d7c555994 100644
--- a/libc/calls/sleep.c
+++ b/libc/calls/sleep.c
@@ -17,32 +17,45 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/assert.h"
+#include "libc/calls/blockcancel.internal.h"
 #include "libc/calls/struct/timespec.h"
 #include "libc/errno.h"
 #include "libc/limits.h"
 #include "libc/sysv/consts/clock.h"
+#include "libc/thread/posixthread.internal.h"
+#include "libc/thread/thread.h"
 #include "libc/time/time.h"
 
 /**
  * Sleeps for particular number of seconds.
  *
+ * This function may be canceled except when using masked mode in which
+ * case cancelation is temporarily disabled, because there is no way to
+ * report the ECANCELED state.
+ *
  * @return 0 if the full time elapsed, otherwise we assume an interrupt
  *     was delivered, in which case the errno condition is ignored, and
  *     this function shall return the number of unslept seconds rounded
- *     using the ceiling function, and finally `-1u` may be returned if
- *     thread was cancelled with `PTHREAD_CANCEL_MASKED` in play
+ *     using the ceiling function
  * @see clock_nanosleep()
  * @cancelationpoint
  * @asyncsignalsafe
  * @norestart
  */
 unsigned sleep(unsigned seconds) {
-  errno_t rc;
+  int cs = -1;
+  errno_t err;
   unsigned unslept;
   struct timespec tv = {seconds};
-  if (!(rc = clock_nanosleep(CLOCK_REALTIME, 0, &tv, &tv))) return 0;
-  if (rc == ECANCELED) return -1u;
-  npassert(rc == EINTR);
+  if (_pthread_self()->pt_flags & PT_MASKED) {
+    cs = _pthread_block_cancelation();
+  }
+  err = clock_nanosleep(CLOCK_REALTIME, 0, &tv, &tv);
+  if (cs != -1) {
+    _pthread_allow_cancelation(cs);
+  }
+  if (!err) return 0;
+  unassert(err == EINTR);
   unslept = tv.tv_sec;
   if (tv.tv_nsec && unslept < UINT_MAX) {
     ++unslept;
diff --git a/libc/calls/struct/sigaction.internal.h b/libc/calls/struct/sigaction.internal.h
index 30e461a88db..d944ad0d159 100644
--- a/libc/calls/struct/sigaction.internal.h
+++ b/libc/calls/struct/sigaction.internal.h
@@ -31,6 +31,12 @@ struct sigaction_netbsd {
   uint32_t sa_flags;
 };
 
+struct sigaction_silicon {
+  void *sa_handler;
+  uint32_t sa_mask[1];
+  uint32_t sa_flags;
+};
+
 struct sigaction_xnu_in {
   void *sa_handler;
   void *sa_restorer;
@@ -50,6 +56,7 @@ union metasigaction {
   struct sigaction_freebsd freebsd;
   struct sigaction_openbsd openbsd;
   struct sigaction_netbsd netbsd;
+  struct sigaction_silicon silicon;
   struct sigaction_xnu_in xnu_in;
   struct sigaction_xnu_out xnu_out;
 };
diff --git a/libc/calls/timespec_sleep.c b/libc/calls/timespec_sleep.c
index 98f13b70db1..36df8f9dd55 100644
--- a/libc/calls/timespec_sleep.c
+++ b/libc/calls/timespec_sleep.c
@@ -22,20 +22,31 @@
 #include "libc/errno.h"
 #include "libc/str/str.h"
 #include "libc/sysv/consts/clock.h"
+#include "libc/thread/posixthread.internal.h"
 
 /**
  * Sleeps for specified delay.
  *
+ * This function may be canceled except when using masked mode in which
+ * case cancelation is temporarily disabled, because there is no way to
+ * report the ECANCELED state.
+ *
  * @return unslept time which may be non-zero if the call was interrupted
+ * @cancelationpoint
  */
 struct timespec timespec_sleep(struct timespec delay) {
-  errno_t rc;
+  int cs = -1;
+  errno_t err;
   struct timespec remain;
-  BLOCK_CANCELATION;
-  bzero(&remain, sizeof(remain));
-  if ((rc = clock_nanosleep(CLOCK_REALTIME, 0, &delay, &remain))) {
-    npassert(rc == EINTR);
+  remain = timespec_zero;
+  if (_pthread_self()->pt_flags & PT_MASKED) {
+    cs = _pthread_block_cancelation();
+  }
+  if ((err = clock_nanosleep(CLOCK_REALTIME, 0, &delay, &remain))) {
+    unassert(err == EINTR);
+  }
+  if (cs != -1) {
+    _pthread_allow_cancelation(cs);
   }
-  ALLOW_CANCELATION;
   return remain;
 }
diff --git a/libc/calls/timespec_sleep_until.c b/libc/calls/timespec_sleep_until.c
index e6a4f6cef86..2040a86f8e2 100644
--- a/libc/calls/timespec_sleep_until.c
+++ b/libc/calls/timespec_sleep_until.c
@@ -33,6 +33,6 @@
 errno_t timespec_sleep_until(struct timespec abs_deadline) {
   errno_t rc;
   rc = clock_nanosleep(CLOCK_REALTIME, TIMER_ABSTIME, &abs_deadline, 0);
-  npassert(!rc || rc == EINTR || rc == ECANCELED);
+  unassert(!rc || rc == EINTR || rc == ECANCELED);
   return rc;
 }
diff --git a/libc/calls/usleep.c b/libc/calls/usleep.c
index 4f827d0cd67..15c37d1d0d9 100644
--- a/libc/calls/usleep.c
+++ b/libc/calls/usleep.c
@@ -17,6 +17,7 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/struct/timespec.h"
+#include "libc/errno.h"
 #include "libc/sysv/consts/clock.h"
 #include "libc/sysv/errfuns.h"
 #include "libc/time/time.h"
@@ -32,7 +33,9 @@
  * @norestart
  */
 int usleep(uint32_t micros) {
+  errno_t err;
   struct timespec ts = timespec_frommicros(micros);
-  if (clock_nanosleep(CLOCK_REALTIME, 0, &ts, 0)) return eintr();
+  err = clock_nanosleep(CLOCK_REALTIME, 0, &ts, 0);
+  if (err) return errno = err, -1;
   return 0;
 }
diff --git a/libc/log/appendresourcereport.c b/libc/log/appendresourcereport.c
index 84f39fd9146..953a635efde 100644
--- a/libc/log/appendresourcereport.c
+++ b/libc/log/appendresourcereport.c
@@ -130,6 +130,9 @@ void AppendResourceReport(char **b, struct rusage *ru, const char *nl) {
   if (ru->ru_nsignals) {
     appends(b, "delivered ");
     AppendUnit(st, ru->ru_nsignals, "signal");
+    if ((ru->ru_nsignals) > 1) {
+      appendw(b, READ16LE("s"));
+    }
     AppendNl(st);
   }
   if (ru->ru_nswap) {
diff --git a/libc/proc/execve-nt.greg.c b/libc/proc/execve-nt.greg.c
index 387e61e18a7..e2989b0df36 100644
--- a/libc/proc/execve-nt.greg.c
+++ b/libc/proc/execve-nt.greg.c
@@ -92,7 +92,6 @@ textwindows int sys_execve_nt(const char *program, char *const argv[],
   if (rc == -1) {
     free(fdspec);
     CloseHandle(hParentProcess);
-    __undescribe_fds(hParentProcess, lpExplicitHandles, dwExplicitHandleCount);
     _pthread_unlock();
     __sig_unblock(m);
     if (GetLastError() == kNtErrorSharingViolation) {
@@ -104,8 +103,8 @@ textwindows int sys_execve_nt(const char *program, char *const argv[],
 
   // give child to libc/proc/proc.c worker thread in parent
   int64_t handle;
-  unassert(!DuplicateHandle(GetCurrentProcess(), pi.hProcess, hParentProcess,
-                            &handle, 0, false, kNtDuplicateSameAccess));
+  unassert(DuplicateHandle(GetCurrentProcess(), pi.hProcess, hParentProcess,
+                           &handle, 0, false, kNtDuplicateSameAccess));
   unassert(!(handle & 0xFFFFFFFFFF000000));
   TerminateThisProcess(0x23000000u | handle);
 }
diff --git a/libc/runtime/syslib.internal.h b/libc/runtime/syslib.internal.h
index de3cc8a4ec2..3f3053b24e8 100644
--- a/libc/runtime/syslib.internal.h
+++ b/libc/runtime/syslib.internal.h
@@ -59,6 +59,15 @@ struct Syslib {
   long (*__sigaction)(int, const void *, void *);
   long (*__pselect)(int, void *, void *, void *, const void *, const void *);
   long (*__mprotect)(void *, size_t, int);
+  /* v5 (2023-10-09) */
+  long (*__sigaltstack)(const void *, void *);
+  long (*__getentropy)(void *, size_t);
+  long (*__sem_open)(const char *, int, uint16_t, unsigned);
+  long (*__sem_unlink)(const char *);
+  long (*__sem_close)(int *);
+  long (*__sem_post)(int *);
+  long (*__sem_wait)(int *);
+  long (*__sem_trywait)(int *);
 };
 
 extern struct Syslib *__syslib;
diff --git a/libc/stdio/printargs.c b/libc/stdio/printargs.c
index 179a2b3aede..24e4c7e4617 100644
--- a/libc/stdio/printargs.c
+++ b/libc/stdio/printargs.c
@@ -45,6 +45,7 @@
 #include "libc/nt/struct/ldrdatatableentry.h"
 #include "libc/nt/struct/startupinfo.h"
 #include "libc/nt/struct/teb.h"
+#include "libc/runtime/clktck.h"
 #include "libc/runtime/internal.h"
 #include "libc/runtime/memtrack.internal.h"
 #include "libc/runtime/runtime.h"
@@ -457,6 +458,7 @@ textstartup void __printargs(const char *prologue) {
   PRINT(" ☼ %s = %d", "geteuid()", geteuid());
   PRINT(" ☼ %s = %d", "getgid()", getgid());
   PRINT(" ☼ %s = %d", "getegid()", getegid());
+  PRINT(" ☼ %s = %d", "CLK_TCK", CLK_TCK);
   PRINT(" ☼ %s = %#s", "__get_tmpdir()", __get_tmpdir());
 #ifdef __x86_64__
   PRINT(" ☼ %s = %#s", "kNtSystemDirectory", kNtSystemDirectory);
diff --git a/libc/thread/pthread_cancel.c b/libc/thread/pthread_cancel.c
index f36f85cf1cb..ec688404014 100644
--- a/libc/thread/pthread_cancel.c
+++ b/libc/thread/pthread_cancel.c
@@ -46,7 +46,9 @@ extern const char systemfive_cancellable[];
 extern const char systemfive_cancellable_end[];
 
 long _pthread_cancel_ack(void) {
-  struct PosixThread *pt = _pthread_self();
+  struct PosixThread *pt;
+  STRACE("_pthread_cancel_ack()");
+  pt = _pthread_self();
   if (!(pt->pt_flags & (PT_NOCANCEL | PT_MASKED)) ||
       (pt->pt_flags & PT_ASYNC)) {
     pthread_exit(PTHREAD_CANCELED);
@@ -58,6 +60,7 @@ long _pthread_cancel_ack(void) {
   return ecanceled();
 }
 
+// the purpose of this routine is to force a blocking system call to end
 static void _pthread_cancel_sig(int sig, siginfo_t *si, void *arg) {
   ucontext_t *ctx = arg;
 
@@ -231,6 +234,7 @@ static errno_t _pthread_cancel_everyone(void) {
  * - `nsync_cv_wait`
  * - `opendir`
  * - `openatemp`, 'mkstemp', etc.
+ * - `sleep`, `usleep`, `nanosleep`, `timespec_sleep`, etc.
  * - `pclose`
  * - `popen`
  * - `fwrite`, `printf`, `fprintf`, `putc`, etc.
@@ -344,15 +348,12 @@ static errno_t _pthread_cancel_everyone(void) {
  * @raise ESRCH if system thread wasn't alive or we lost a race
  */
 errno_t pthread_cancel(pthread_t thread) {
-  errno_t err;
   struct PosixThread *arg;
   if ((arg = (struct PosixThread *)thread)) {
-    err = _pthread_cancel_single(arg);
+    return _pthread_cancel_single(arg);
   } else {
-    err = _pthread_cancel_everyone();
+    return _pthread_cancel_everyone();
   }
-  STRACE("pthread_cancel(%d) → %s", _pthread_tid(arg), DescribeErrno(err));
-  return err;
 }
 
 /**
diff --git a/libc/thread/sem_open.c b/libc/thread/sem_open.c
index cbac0ead01d..89c68fc44e0 100644
--- a/libc/thread/sem_open.c
+++ b/libc/thread/sem_open.c
@@ -20,6 +20,7 @@
 #include "libc/calls/blockcancel.internal.h"
 #include "libc/calls/calls.h"
 #include "libc/calls/struct/stat.h"
+#include "libc/calls/syscall-sysv.internal.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/intrin/atomic.h"
@@ -27,6 +28,7 @@
 #include "libc/limits.h"
 #include "libc/mem/mem.h"
 #include "libc/runtime/runtime.h"
+#include "libc/runtime/syslib.internal.h"
 #include "libc/str/str.h"
 #include "libc/sysv/consts/at.h"
 #include "libc/sysv/consts/map.h"
@@ -173,15 +175,32 @@ sem_t *sem_open(const char *name, int oflag, ...) {
   struct Semaphore *s;
   char pathbuf[PATH_MAX];
   unsigned mode = 0, value = 0;
+
+  va_start(va, oflag);
+  mode = va_arg(va, unsigned);
+  value = va_arg(va, unsigned);
+  va_end(va);
+
+#if 0
+  if (IsXnuSilicon()) {
+    long kernel;
+    if (!(sem = calloc(1, sizeof(sem_t)))) return SEM_FAILED;
+    sem->sem_magic = SEM_MAGIC_KERNEL;
+    kernel = _sysret(__syslib->__sem_open(name, oflag, mode, value));
+    if (kernel == -1) {
+      free(sem);
+      return SEM_FAILED;
+    }
+    sem->sem_magic = SEM_MAGIC_KERNEL;
+    sem->sem_kernel = (int *)kernel;
+  }
+#endif
+
   if (oflag & ~(O_CREAT | O_EXCL)) {
     einval();
     return SEM_FAILED;
   }
   if (oflag & O_CREAT) {
-    va_start(va, oflag);
-    mode = va_arg(va, unsigned);
-    value = va_arg(va, unsigned);
-    va_end(va);
     if (value > SEM_VALUE_MAX) {
       einval();
       return SEM_FAILED;
@@ -250,6 +269,14 @@ int sem_close(sem_t *sem) {
   int prefs;
   bool unmap, delete;
   struct Semaphore *s, **p;
+
+#if 0
+  if (IsXnuSilicon()) {
+    npassert(sem->sem_magic == SEM_MAGIC_KERNEL);
+    return _sysret(__syslib->__sem_close(sem->sem_kernel));
+  }
+#endif
+
   npassert(sem->sem_magic == SEM_MAGIC_NAMED);
   sem_open_init();
   sem_open_lock();
@@ -298,6 +325,13 @@ int sem_unlink(const char *name) {
   int rc, e = errno;
   struct Semaphore *s;
   char pathbuf[PATH_MAX];
+
+#if 0
+  if (IsXnuSilicon()) {
+    return _sysret(__syslib->__sem_unlink(name));
+  }
+#endif
+
   if (!(path = sem_path_np(name, pathbuf, sizeof(pathbuf)))) return -1;
   if ((rc = unlink(path)) == -1 && IsWindows() && errno == EACCES) {
     sem_open_init();
diff --git a/libc/thread/sem_post.c b/libc/thread/sem_post.c
index 4ed66ec4509..0cedcc6c1f5 100644
--- a/libc/thread/sem_post.c
+++ b/libc/thread/sem_post.c
@@ -18,9 +18,12 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/assert.h"
 #include "libc/calls/calls.h"
+#include "libc/calls/syscall-sysv.internal.h"
+#include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/intrin/atomic.h"
 #include "libc/limits.h"
+#include "libc/runtime/syslib.internal.h"
 #include "libc/sysv/errfuns.h"
 #include "libc/thread/semaphore.h"
 #include "third_party/nsync/futex.internal.h"
@@ -33,6 +36,13 @@
  */
 int sem_post(sem_t *sem) {
   int rc, old, wakeups;
+
+#if 0
+  if (IsXnuSilicon() && sem->sem_magic == SEM_MAGIC_KERNEL) {
+    return _sysret(__syslib->__sem_post(sem->sem_kernel));
+  }
+#endif
+
   old = atomic_fetch_add_explicit(&sem->sem_value, 1, memory_order_acq_rel);
   unassert(old > INT_MIN);
   if (old >= 0) {
diff --git a/libc/thread/sem_timedwait.c b/libc/thread/sem_timedwait.c
index d2d117482f0..f2a278147b8 100644
--- a/libc/thread/sem_timedwait.c
+++ b/libc/thread/sem_timedwait.c
@@ -17,12 +17,17 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/assert.h"
+#include "libc/calls/calls.h"
 #include "libc/calls/cp.internal.h"
 #include "libc/calls/struct/timespec.h"
 #include "libc/calls/struct/timespec.internal.h"
+#include "libc/calls/syscall-sysv.internal.h"
+#include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/intrin/atomic.h"
+#include "libc/intrin/weaken.h"
 #include "libc/limits.h"
+#include "libc/runtime/syslib.internal.h"
 #include "libc/sysv/errfuns.h"
 #include "libc/thread/semaphore.h"
 #include "libc/thread/thread.h"
@@ -52,9 +57,48 @@ static void sem_timedwait_cleanup(void *arg) {
  * @cancelationpoint
  */
 int sem_timedwait(sem_t *sem, const struct timespec *abstime) {
-  int e, i, v, rc;
+  int i, v, rc, e = errno;
+
+#if 0
+  if (IsXnuSilicon() && sem->sem_magic == SEM_MAGIC_KERNEL) {
+    if (!abstime) {
+      if (_weaken(pthread_testcancel_np) &&  //
+          _weaken(pthread_testcancel_np)()) {
+        return ecanceled();
+      }
+      rc = _sysret(__syslib->__sem_wait(sem->sem_kernel));
+      if (rc == -1 && errno == EINTR &&      //
+          _weaken(pthread_testcancel_np) &&  //
+          _weaken(pthread_testcancel_np)()) {
+        return ecanceled();
+      }
+      return rc;
+    }
+    for (;;) {
+      if (_weaken(pthread_testcancel_np) &&  //
+          _weaken(pthread_testcancel_np)()) {
+        return ecanceled();
+      }
+      rc = _sysret(__syslib->__sem_trywait(sem->sem_kernel));
+      if (!rc) return 0;
+      if (errno == EINTR &&                  //
+          _weaken(pthread_testcancel_np) &&  //
+          _weaken(pthread_testcancel_np)()) {
+        return ecanceled();
+      }
+      if (errno != EAGAIN) return -1;
+      errno = e;
+      struct timespec now = timespec_real();
+      if (timespec_cmp(*abstime, now) >= 0) {
+        return etimedout();
+      }
+      if (usleep(10 * 1000) == -1) {
+        return -1;
+      }
+    }
+  }
+#endif
 
-  e = errno;
   for (i = 0; i < 7; ++i) {
     rc = sem_trywait(sem);
     if (!rc) {
diff --git a/libc/thread/sem_trywait.c b/libc/thread/sem_trywait.c
index d76a6402a87..8f49d081243 100644
--- a/libc/thread/sem_trywait.c
+++ b/libc/thread/sem_trywait.c
@@ -18,9 +18,12 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/assert.h"
 #include "libc/calls/calls.h"
+#include "libc/calls/syscall-sysv.internal.h"
+#include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/intrin/atomic.h"
 #include "libc/limits.h"
+#include "libc/runtime/syslib.internal.h"
 #include "libc/sysv/errfuns.h"
 #include "libc/thread/semaphore.h"
 
@@ -34,6 +37,13 @@
  */
 int sem_trywait(sem_t *sem) {
   int v;
+
+#if 0
+  if (IsXnuSilicon() && sem->sem_magic == SEM_MAGIC_KERNEL) {
+    return _sysret(__syslib->__sem_trywait(sem->sem_kernel));
+  }
+#endif
+
   v = atomic_load_explicit(&sem->sem_value, memory_order_relaxed);
   do {
     unassert(v > INT_MIN);
diff --git a/libc/thread/semaphore.h b/libc/thread/semaphore.h
index 4e759e1c80a..5f0c2cb15ab 100644
--- a/libc/thread/semaphore.h
+++ b/libc/thread/semaphore.h
@@ -8,6 +8,7 @@ COSMOPOLITAN_C_START_
 #define SEM_FAILED        ((sem_t *)0)
 #define SEM_MAGIC_NAMED   0xDEADBEEFu
 #define SEM_MAGIC_UNNAMED 0xFEEDABEEu
+#define SEM_MAGIC_KERNEL  0xCAFEBABEu
 
 typedef struct {
   union {
@@ -21,6 +22,7 @@ typedef struct {
       int sem_pid;         /* unnamed only */
       bool sem_lazydelete; /* named only */
       bool sem_pshared;
+      int *sem_kernel;
     };
     void *sem_space[32];
   };
diff --git a/test/libc/thread/pthread_cancel_test.c b/test/libc/thread/pthread_cancel_test.c
index c15298ec3c0..ca4a246a44e 100644
--- a/test/libc/thread/pthread_cancel_test.c
+++ b/test/libc/thread/pthread_cancel_test.c
@@ -18,6 +18,7 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/atomic.h"
 #include "libc/calls/calls.h"
+#include "libc/calls/struct/sigaction.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/intrin/kprintf.h"
@@ -26,6 +27,7 @@
 #include "libc/nexgen32e/nexgen32e.h"
 #include "libc/runtime/internal.h"
 #include "libc/runtime/runtime.h"
+#include "libc/sysv/consts/sig.h"
 #include "libc/testlib/testlib.h"
 #include "libc/thread/thread.h"
 #include "libc/thread/thread2.h"
@@ -283,3 +285,28 @@ TEST(pthread_cancel, self_asynchronous_takesImmediateEffect) {
   ASSERT_SYS(0, 0, close(pfds[1]));
   ASSERT_SYS(0, 0, close(pfds[0]));
 }
+
+atomic_bool was_completed;
+
+void WaitUntilReady(void) {
+  while (!ready) pthread_yield();
+  ASSERT_EQ(0, errno);
+  ASSERT_SYS(0, 0, usleep(1000));
+}
+
+void *SleepWorker(void *arg) {
+  pthread_setcancelstate(PTHREAD_CANCEL_MASKED, 0);
+  ready = true;
+  ASSERT_SYS(ECANCELED, -1, usleep(30 * 1e6));
+  was_completed = true;
+  return 0;
+}
+
+TEST(pthread_cancel, canInterruptSleepOperation) {
+  pthread_t th;
+  ASSERT_EQ(0, pthread_create(&th, 0, SleepWorker, 0));
+  WaitUntilReady();
+  ASSERT_EQ(0, pthread_cancel(th));
+  ASSERT_EQ(0, pthread_join(th, 0));
+  ASSERT_TRUE(was_completed);
+}
diff --git a/test/libc/thread/pthread_kill_test.c b/test/libc/thread/pthread_kill_test.c
index 1f4e5ac70e3..679e4460f15 100644
--- a/test/libc/thread/pthread_kill_test.c
+++ b/test/libc/thread/pthread_kill_test.c
@@ -21,7 +21,6 @@
 #include "libc/calls/struct/sigaction.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
-#include "libc/intrin/kprintf.h"
 #include "libc/runtime/runtime.h"
 #include "libc/sock/sock.h"
 #include "libc/sock/struct/sockaddr.h"
@@ -85,7 +84,6 @@ TEST(pthread_kill, canInterruptSleepOperation) {
   signal(SIGUSR1, old);
 }
 
-#if 0
 void *ReadWorker(void *arg) {
   char buf[8] = {0};
   ready = true;
@@ -324,4 +322,3 @@ TEST(pthread_kill, canInterruptSigsuspend) {
   ASSERT_SYS(0, 0, sigprocmask(SIG_SETMASK, &oldss, 0));
   signal(SIGUSR1, oldsig);
 }
-#endif
diff --git a/third_party/python/Modules/_multiprocessing/semaphore.c b/third_party/python/Modules/_multiprocessing/semaphore.c
index 1c18450b7a8..3c3d29a2fd5 100644
--- a/third_party/python/Modules/_multiprocessing/semaphore.c
+++ b/third_party/python/Modules/_multiprocessing/semaphore.c
@@ -207,7 +207,7 @@ semlock_release(SemLockObject *self, PyObject *args)
 #endif
 
 #ifndef HAVE_SEM_TIMEDWAIT
-#  define sem_timedwait(sem,deadline) sem_timedwait_save(sem,deadline,_save)
+#  define sem_timedwait_(sem,deadline) sem_timedwait_save(sem,deadline,_save)
 
 static int
 sem_timedwait_save(sem_t *sem, struct timespec *deadline, PyThreadState *_save)
diff --git a/tool/build/runit.c b/tool/build/runit.c
index 7ec48fee4f5..33380a125cf 100644
--- a/tool/build/runit.c
+++ b/tool/build/runit.c
@@ -25,7 +25,6 @@
 #include "libc/calls/struct/timespec.h"
 #include "libc/dns/dns.h"
 #include "libc/errno.h"
-#include "libc/fmt/conv.h"
 #include "libc/fmt/libgen.h"
 #include "libc/intrin/bits.h"
 #include "libc/intrin/kprintf.h"
@@ -33,9 +32,7 @@
 #include "libc/limits.h"
 #include "libc/log/check.h"
 #include "libc/log/log.h"
-#include "libc/macros.internal.h"
 #include "libc/mem/gc.h"
-#include "libc/mem/gc.internal.h"
 #include "libc/mem/mem.h"
 #include "libc/runtime/runtime.h"
 #include "libc/sock/ipclassify.internal.h"
@@ -51,12 +48,8 @@
 #include "libc/sysv/consts/prot.h"
 #include "libc/sysv/consts/sig.h"
 #include "libc/sysv/consts/sock.h"
-#include "libc/time/time.h"
-#include "libc/x/x.h"
 #include "libc/x/xasprintf.h"
-#include "libc/x/xsigaction.h"
 #include "net/https/https.h"
-#include "third_party/mbedtls/debug.h"
 #include "third_party/mbedtls/net_sockets.h"
 #include "third_party/mbedtls/ssl.h"
 #include "third_party/zlib/zlib.h"
diff --git a/tool/viz/clock_nanosleep_accuracy.c b/tool/viz/clock_nanosleep_accuracy.c
index c21f483e048..b4fb98f0700 100644
--- a/tool/viz/clock_nanosleep_accuracy.c
+++ b/tool/viz/clock_nanosleep_accuracy.c
@@ -26,11 +26,6 @@
 #define MAXIMUM    1e9
 #define ITERATIONS 10
 
-void WarmUp(void) {
-  struct timespec wf = {0, 1};
-  npassert(!clock_nanosleep(CLOCK_REALTIME, 0, &wf, 0));
-}
-
 void TestSleepRealRelative(void) {
   printf("\n");
   printf("testing: clock_nanosleep(CLOCK_REALTIME) with relative "
@@ -68,7 +63,6 @@ void TestSleepMonoRelative(void) {
 }
 
 int main(int argc, char *argv[]) {
-  WarmUp();
   TestSleepRealRelative();
   TestSleepMonoRelative();
 }
diff --git a/tool/viz/setitimer_accuracy.c b/tool/viz/setitimer_accuracy.c
new file mode 100644
index 00000000000..64fb0836fa4
--- /dev/null
+++ b/tool/viz/setitimer_accuracy.c
@@ -0,0 +1,61 @@
+/*-*- 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/calls/calls.h"
+#include "libc/calls/struct/itimerval.h"
+#include "libc/calls/struct/sigaction.h"
+#include "libc/calls/struct/timespec.h"
+#include "libc/calls/struct/timeval.h"
+#include "libc/fmt/itoa.h"
+#include "libc/sysv/consts/itimer.h"
+#include "libc/sysv/consts/sig.h"
+
+#define HZ 120
+
+struct timeval start;
+struct timeval expect;
+struct timeval interval = {0, 1e6 / HZ};
+
+void OnTick(int sig) {
+  char ibuf[27];
+  struct timeval now = timeval_real();
+  switch (timeval_cmp(now, expect)) {
+    case 0:
+      tinyprint(1, "100% precise\n", NULL);
+      break;
+    case -1:
+      FormatInt64Thousands(ibuf, timeval_tomicros(timeval_sub(expect, now)));
+      tinyprint(1, ibuf, " µs early\n", NULL);
+      break;
+    case +1:
+      FormatInt64Thousands(ibuf, timeval_tomicros(timeval_sub(now, expect)));
+      tinyprint(1, ibuf, " µs late\n", NULL);
+      break;
+    default:
+      __builtin_unreachable();
+  }
+  expect = timeval_add(expect, interval);
+}
+
+int main(int argc, char *argv[]) {
+  start = timeval_real();
+  expect = timeval_add(start, interval);
+  signal(SIGALRM, OnTick);
+  setitimer(ITIMER_REAL, &(struct itimerval){interval, interval}, 0);
+  for (;;) pause();
+}