fusl/src/thread/pthread_cancel.c

#define _GNU_SOURCE
#include <string.h>
#include "pthread_impl.h"
#include "syscall.h"
#include "libc.h"

__attribute__((__visibility__("hidden"))) long __cancel(), __syscall_cp_asm(),
    __syscall_cp_c();

long __cancel() {
  pthread_t self = __pthread_self();
  if (self->canceldisable == PTHREAD_CANCEL_ENABLE || self->cancelasync)
    pthread_exit(PTHREAD_CANCELED);
  self->canceldisable = PTHREAD_CANCEL_DISABLE;
  return -ECANCELED;
}

long __syscall_cp_asm(volatile void*,
                      syscall_arg_t,
                      syscall_arg_t,
                      syscall_arg_t,
                      syscall_arg_t,
                      syscall_arg_t,
                      syscall_arg_t,
                      syscall_arg_t);

long __syscall_cp_c(syscall_arg_t nr,
                    syscall_arg_t u,
                    syscall_arg_t v,
                    syscall_arg_t w,
                    syscall_arg_t x,
                    syscall_arg_t y,
                    syscall_arg_t z) {
  pthread_t self;
  long r;
  int st;

  if ((st = (self = __pthread_self())->canceldisable) &&
      (st == PTHREAD_CANCEL_DISABLE || nr == SYS_close))
    return __syscall(nr, u, v, w, x, y, z);

  r = __syscall_cp_asm(&self->cancel, nr, u, v, w, x, y, z);
  if (r == -EINTR && nr != SYS_close && self->cancel &&
      self->canceldisable != PTHREAD_CANCEL_DISABLE)
    r = __cancel();
  return r;
}

static void _sigaddset(sigset_t* set, int sig) {
  unsigned s = sig - 1;
  set->__bits[s / 8 / sizeof *set->__bits] |=
      1UL << (s & 8 * sizeof *set->__bits - 1);
}

__attribute__((__visibility__("hidden"))) extern const char __cp_begin[1],
    __cp_end[1], __cp_cancel[1];

static void cancel_handler(int sig, siginfo_t* si, void* ctx) {
  pthread_t self = __pthread_self();
  ucontext_t* uc = ctx;
  uintptr_t pc = uc->uc_mcontext.MC_PC;

  a_barrier();
  if (!self->cancel || self->canceldisable == PTHREAD_CANCEL_DISABLE)
    return;

  _sigaddset(&uc->uc_sigmask, SIGCANCEL);

  if (self->cancelasync ||
      (pc >= (uintptr_t)__cp_begin && pc < (uintptr_t)__cp_end)) {
    uc->uc_mcontext.MC_PC = (uintptr_t)__cp_cancel;
    return;
  }

  __syscall(SYS_tkill, self->tid, SIGCANCEL);
}

void __testcancel() {
  pthread_t self = __pthread_self();
  if (self->cancel && !self->canceldisable)
    __cancel();
}

static void init_cancellation() {
  struct sigaction sa = {.sa_flags = SA_SIGINFO | SA_RESTART,
                         .sa_sigaction = cancel_handler};
  memset(&sa.sa_mask, -1, _NSIG / 8);
  __libc_sigaction(SIGCANCEL, &sa, 0);
}

int pthread_cancel(pthread_t t) {
  static int init;
  if (!init) {
    init_cancellation();
    init = 1;
  }
  a_store(&t->cancel, 1);
  if (t == pthread_self() && !t->cancelasync)
    return 0;
  return pthread_kill(t, SIGCANCEL);
}