ocaml/otherlibs/systhreads/posix.c

/***********************************************************************/
/*                                                                     */
/*                             Objective Caml                          */
/*                                                                     */
/*         Xavier Leroy and Damien Doligez, INRIA Rocquencourt         */
/*                                                                     */
/*  Copyright 1995 Institut National de Recherche en Informatique et   */
/*  en Automatique.  All rights reserved.  This file is distributed    */
/*  under the terms of the GNU Library General Public License, with    */
/*  the special exception on linking described in file ../../LICENSE.  */
/*                                                                     */
/***********************************************************************/

/* $Id$ */

/* Thread interface for POSIX 1003.1c threads */

#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#ifdef __sun
#define _POSIX_PTHREAD_SEMANTICS
#endif
#include <signal.h>
#include <sys/time.h>
#include "alloc.h"
#include "backtrace.h"
#include "callback.h"
#include "custom.h"
#include "fail.h"
#include "io.h"
#include "memory.h"
#include "misc.h"
#include "mlvalues.h"
#include "printexc.h"
#include "roots.h"
#include "signals.h"
#ifdef NATIVE_CODE
#include "stack.h"
#else
#include "stacks.h"
#endif
#include "sys.h"

/* Initial size of stack when a thread is created (4 Ko) */
#define Thread_stack_size (Stack_size / 4)

/* Max computation time before rescheduling, in microseconds (50ms) */
#define Thread_timeout 50000

/* The ML value describing a thread (heap-allocated) */

struct caml_thread_descr {
  value ident;                  /* Unique integer ID */
  value start_closure;          /* The closure to start this thread */
  value terminated;             /* Mutex held while the thread is running */
};

#define Ident(v) (((struct caml_thread_descr *)(v))->ident)
#define Start_closure(v) (((struct caml_thread_descr *)(v))->start_closure)
#define Terminated(v) (((struct caml_thread_descr *)(v))->terminated)

/* The infos on threads (allocated via malloc()) */

struct caml_thread_struct {
  pthread_t pthread;            /* The Posix thread id */
  value descr;                  /* The heap-allocated descriptor (root) */
  struct caml_thread_struct * next;  /* Double linking of running threads */
  struct caml_thread_struct * prev;
#ifdef NATIVE_CODE
  char * bottom_of_stack;       /* Saved value of caml_bottom_of_stack */
  unsigned long last_retaddr;   /* Saved value of caml_last_return_address */
  value * gc_regs;              /* Saved value of caml_gc_regs */
  char * exception_pointer;     /* Saved value of caml_exception_pointer */
  struct caml__roots_block * local_roots; /* Saved value of local_roots */
#else
  value * stack_low;            /* The execution stack for this thread */
  value * stack_high;
  value * stack_threshold;
  value * sp;                   /* Saved value of extern_sp for this thread */
  value * trapsp;               /* Saved value of trapsp for this thread */
  struct caml__roots_block * local_roots; /* Saved value of local_roots */
  struct longjmp_buffer * external_raise; /* Saved external_raise */
  int backtrace_pos;            /* Saved backtrace_pos */
  code_t * backtrace_buffer;    /* Saved backtrace_buffer */
  value backtrace_last_exn;     /* Saved backtrace_last_exn (root) */
#endif
};

typedef struct caml_thread_struct * caml_thread_t;

/* The descriptor for the currently executing thread */

static caml_thread_t curr_thread = NULL;

/* The global mutex used to ensure that at most one thread is running
   Caml code */
static pthread_mutex_t caml_mutex;

/* The key used for storing the thread descriptor in the specific data
   of the corresponding Posix thread. */
static pthread_key_t thread_descriptor_key;

/* The key used for unlocking I/O channels on exceptions */
static pthread_key_t last_channel_locked_key;

/* Identifier for next thread creation */
static long thread_next_ident = 0;

/* Forward declarations */

value caml_threadstatus_new (void);
void caml_threadstatus_terminate (value);
int caml_threadstatus_wait (value);
static void caml_pthread_check (int, char *);

/* Hook for scanning the stacks of the other threads */

static void (*prev_scan_roots_hook) (scanning_action);

static void caml_thread_scan_roots(scanning_action action)
{
  caml_thread_t th;

  th = curr_thread;
  do {
    (*action)(th->descr, &th->descr);
#ifndef NATIVE_CODE
    (*action)(th->backtrace_last_exn, &th->backtrace_last_exn);
#endif
    /* Don't rescan the stack of the current thread, it was done already */
    if (th != curr_thread) {
#ifdef NATIVE_CODE
      if (th->bottom_of_stack != NULL)
        do_local_roots(action, th->bottom_of_stack, th->last_retaddr,
                       th->gc_regs, th->local_roots);
#else
      do_local_roots(action, th->sp, th->stack_high, th->local_roots);
#endif
    }
    th = th->next;
  } while (th != curr_thread);
  /* Hook */
  if (prev_scan_roots_hook != NULL) (*prev_scan_roots_hook)(action);
}

/* Hooks for enter_blocking_section and leave_blocking_section */

static void (*prev_enter_blocking_section_hook) () = NULL;
static void (*prev_leave_blocking_section_hook) () = NULL;

static void caml_thread_enter_blocking_section(void)
{
  if (prev_enter_blocking_section_hook != NULL)
    (*prev_enter_blocking_section_hook)();
  /* Save the stack-related global variables in the thread descriptor
     of the current thread */
#ifdef NATIVE_CODE
  curr_thread->bottom_of_stack = caml_bottom_of_stack;
  curr_thread->last_retaddr = caml_last_return_address;
  curr_thread->gc_regs = caml_gc_regs;
  curr_thread->exception_pointer = caml_exception_pointer;
  curr_thread->local_roots = local_roots;
#else
  curr_thread->stack_low = stack_low;
  curr_thread->stack_high = stack_high;
  curr_thread->stack_threshold = stack_threshold;
  curr_thread->sp = extern_sp;
  curr_thread->trapsp = trapsp;
  curr_thread->local_roots = local_roots;
  curr_thread->external_raise = external_raise;
  curr_thread->backtrace_pos = backtrace_pos;
  curr_thread->backtrace_buffer = backtrace_buffer;
  curr_thread->backtrace_last_exn = backtrace_last_exn;
#endif
  /* Release the global mutex */
  pthread_mutex_unlock(&caml_mutex);
}

static void caml_thread_leave_blocking_section(void)
{
  /* Re-acquire the global mutex */
  pthread_mutex_lock(&caml_mutex);
  /* Update curr_thread to point to the thread descriptor corresponding
     to the thread currently executing */
  curr_thread = pthread_getspecific(thread_descriptor_key);
  /* Restore the stack-related global variables */
#ifdef NATIVE_CODE
  caml_bottom_of_stack= curr_thread->bottom_of_stack;
  caml_last_return_address = curr_thread->last_retaddr;
  caml_gc_regs = curr_thread->gc_regs;
  caml_exception_pointer = curr_thread->exception_pointer;
  local_roots = curr_thread->local_roots;
#else
  stack_low = curr_thread->stack_low;
  stack_high = curr_thread->stack_high;
  stack_threshold = curr_thread->stack_threshold;
  extern_sp = curr_thread->sp;
  trapsp = curr_thread->trapsp;
  local_roots = curr_thread->local_roots;
  external_raise = curr_thread->external_raise;
  backtrace_pos = curr_thread->backtrace_pos;
  backtrace_buffer = curr_thread->backtrace_buffer;
  backtrace_last_exn = curr_thread->backtrace_last_exn;
#endif
  if (prev_leave_blocking_section_hook != NULL)
    (*prev_leave_blocking_section_hook)();
}

/* Hooks for I/O locking */

static void caml_io_mutex_free(struct channel *chan)
{
  pthread_mutex_t * mutex = chan->mutex;
  if (mutex != NULL) {
    pthread_mutex_destroy(mutex);
    stat_free((char *) mutex);
  }
}

static void caml_io_mutex_lock(struct channel *chan)
{
  if (chan->mutex == NULL) {
    pthread_mutex_t * mutex =
      (pthread_mutex_t *) stat_alloc(sizeof(pthread_mutex_t));
    pthread_mutex_init(mutex, NULL);
    chan->mutex = (void *) mutex;
  }
  enter_blocking_section();
  pthread_mutex_lock(chan->mutex);
  /* Problem: if a signal occurs at this point,
     and the signal handler raises an exception, we will not
     unlock the mutex.  The alternative (doing the setspecific
     before locking the mutex is also incorrect, since we could
     then unlock a mutex that is unlocked or locked by someone else. */
  pthread_setspecific(last_channel_locked_key, (void *) chan);
  leave_blocking_section();
}

static void caml_io_mutex_unlock(struct channel *chan)
{
  pthread_mutex_unlock(chan->mutex);
  pthread_setspecific(last_channel_locked_key, NULL);
}

static void caml_io_mutex_unlock_exn(void)
{
  struct channel * chan = pthread_getspecific(last_channel_locked_key);
  if (chan != NULL) caml_io_mutex_unlock(chan);
}

/* The "tick" thread fakes a SIGVTALRM signal at regular intervals. */

static void * caml_thread_tick(void * arg)
{
  struct timeval timeout;
  sigset_t mask;

  /* Block all signals so that we don't try to execute a Caml signal handler */
  sigfillset(&mask);
  pthread_sigmask(SIG_BLOCK, &mask, NULL);
  while(1) {
    /* select() seems to be the most efficient way to suspend the
       thread for sub-second intervals */
    timeout.tv_sec = 0;
    timeout.tv_usec = Thread_timeout;
    select(0, NULL, NULL, NULL, &timeout);
    /* This signal should never cause a callback, so don't go through
       handle_signal(), tweak the global variable directly. */
    if (pending_signal == 0) pending_signal = SIGVTALRM;
#ifdef NATIVE_CODE
    young_limit = young_end;
#else
    something_to_do = 1;
#endif
  }
  return NULL;                  /* prevents compiler warning */
}

/* Initialize the thread machinery */

value caml_thread_initialize(value unit)   /* ML */
{
  pthread_t tick_pthread;
  pthread_attr_t attr;
  value mu = Val_unit;
  value descr;

  Begin_root (mu);
    /* Initialize the main mutex */
    caml_pthread_check(pthread_mutex_init(&caml_mutex, NULL),
                       "Thread.init");
    pthread_mutex_lock(&caml_mutex);
    /* Initialize the keys */
    pthread_key_create(&thread_descriptor_key, NULL);
    pthread_key_create(&last_channel_locked_key, NULL);
    /* Create and initialize the termination semaphore */
    mu = caml_threadstatus_new();
    /* Create a descriptor for the current thread */
    descr = alloc_small(3, 0);
    Ident(descr) = Val_long(thread_next_ident);
    Start_closure(descr) = Val_unit;
    Terminated(descr) = mu;
    thread_next_ident++;
    /* Create an info block for the current thread */
    curr_thread =
      (caml_thread_t) stat_alloc(sizeof(struct caml_thread_struct));
    curr_thread->pthread = pthread_self();
    curr_thread->descr = descr;
    curr_thread->next = curr_thread;
    curr_thread->prev = curr_thread;
    /* The stack-related fields will be filled in at the next
       enter_blocking_section */
    /* Associate the thread descriptor with the thread */
    pthread_setspecific(thread_descriptor_key, (void *) curr_thread);
    /* Set up the hooks */
    prev_scan_roots_hook = scan_roots_hook;
    scan_roots_hook = caml_thread_scan_roots;
    prev_enter_blocking_section_hook = enter_blocking_section_hook;
    enter_blocking_section_hook = caml_thread_enter_blocking_section;
    prev_leave_blocking_section_hook = leave_blocking_section_hook;
    leave_blocking_section_hook = caml_thread_leave_blocking_section;
    channel_mutex_free = caml_io_mutex_free;
    channel_mutex_lock = caml_io_mutex_lock;
    channel_mutex_unlock = caml_io_mutex_unlock;
    channel_mutex_unlock_exn = caml_io_mutex_unlock_exn;
    /* Fork the tick thread */
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
    caml_pthread_check(
        pthread_create(&tick_pthread, &attr, caml_thread_tick, NULL),
        "Thread.init");
  End_roots();
  return Val_unit;
}

/* Create a thread */

static void * caml_thread_start(void * arg)
{
  caml_thread_t th = (caml_thread_t) arg;
  value clos;

  /* Associate the thread descriptor with the thread */
  pthread_setspecific(thread_descriptor_key, (void *) th);
  /* Acquire the global mutex and set up the stack variables */
  leave_blocking_section();
  /* Callback the closure */
  clos = Start_closure(th->descr);
  modify(&(Start_closure(th->descr)), Val_unit);
  callback_exn(clos, Val_unit);
  /* Signal that the thread has terminated */
  caml_threadstatus_terminate(Terminated(th->descr));
  /* Remove th from the doubly-linked list of threads */
  th->next->prev = th->prev;
  th->prev->next = th->next;
  /* Release the main mutex (forever) */
  async_signal_mode = 1;
  pthread_mutex_unlock(&caml_mutex);
#ifndef NATIVE_CODE
  /* Free the memory resources */
  stat_free(th->stack_low);
  if (th->backtrace_buffer != NULL) free(th->backtrace_buffer);
#endif
  /* Free the thread descriptor */
  stat_free(th);
  /* The thread now stops running */
  return NULL;
}  

value caml_thread_new(value clos)          /* ML */
{
  pthread_attr_t attr;
  caml_thread_t th;
  value mu = Val_unit;
  value descr;
  int err;

  Begin_roots2 (clos, mu)
    /* Create and initialize the termination semaphore */
    mu = caml_threadstatus_new();
    /* Create a descriptor for the new thread */
    descr = alloc_small(3, 0);
    Ident(descr) = Val_long(thread_next_ident);
    Start_closure(descr) = clos;
    Terminated(descr) = mu;
    thread_next_ident++;
    /* Create an info block for the current thread */
    th = (caml_thread_t) stat_alloc(sizeof(struct caml_thread_struct));
    th->descr = descr;
#ifdef NATIVE_CODE
    th->bottom_of_stack = NULL;
    th->exception_pointer = NULL;
    th->local_roots = NULL;
#else
    /* Allocate the stacks */
    th->stack_low = (value *) stat_alloc(Thread_stack_size);
    th->stack_high = th->stack_low + Thread_stack_size / sizeof(value);
    th->stack_threshold = th->stack_low + Stack_threshold / sizeof(value);
    th->sp = th->stack_high;
    th->trapsp = th->stack_high;
    th->local_roots = NULL;
    th->external_raise = NULL;
    th->backtrace_pos = 0;
    th->backtrace_buffer = NULL;
    th->backtrace_last_exn = Val_unit;
#endif
    /* Add thread info block to the list of threads */
    th->next = curr_thread->next;
    th->prev = curr_thread;
    curr_thread->next->prev = th;
    curr_thread->next = th;
    /* Fork the new thread */
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
    err = pthread_create(&th->pthread, &attr, caml_thread_start, (void *) th);
    if (err != 0) {
      /* Fork failed, remove thread info block from list of threads */
      th->next->prev = curr_thread;
      curr_thread->next = th->next;
#ifndef NATIVE_CODE
      stat_free(th->stack_low);
#endif
      stat_free(th);
      caml_pthread_check(err, "Thread.create");
    }
  End_roots();
  return descr;
}

/* Return the current thread */

value caml_thread_self(value unit)         /* ML */
{
  if (curr_thread == NULL) invalid_argument("Thread.self: not initialized");
  return curr_thread->descr;
}

/* Return the identifier of a thread */

value caml_thread_id(value th)          /* ML */
{
  return Ident(th);
}

/* Print uncaught exception and backtrace */

value caml_thread_uncaught_exception(value exn)  /* ML */
{
  char * msg = format_caml_exception(exn);
  fprintf(stderr, "Thread %d killed on uncaught exception %s\n",
          Int_val(Ident(curr_thread->descr)), msg);
  free(msg);
#ifndef NATIVE_CODE
  if (backtrace_active) print_exception_backtrace();
#endif
  fflush(stderr);
  return Val_unit;
}

/* Allow re-scheduling */

value caml_thread_yield(value unit)        /* ML */
{
  enter_blocking_section();
  sched_yield();
  leave_blocking_section();
  return Val_unit;
}

/* Suspend the current thread until another thread terminates */

value caml_thread_join(value th)          /* ML */
{
  int retcode = caml_threadstatus_wait(Terminated(th));
  caml_pthread_check(retcode, "Thread.join");
  return Val_unit;
}

/* Mutex operations */

#define Mutex_val(v) (* ((pthread_mutex_t **) Data_custom_val(v)))
#define Max_mutex_number 1000

static void caml_mutex_finalize(value wrapper)
{
  pthread_mutex_t * mut = Mutex_val(wrapper);
  pthread_mutex_destroy(mut);
  stat_free(mut);
}

static int caml_mutex_condition_compare(value wrapper1, value wrapper2)
{
  pthread_mutex_t * mut1 = Mutex_val(wrapper1);
  pthread_mutex_t * mut2 = Mutex_val(wrapper2);
  return mut1 == mut2 ? 0 : mut1 < mut2 ? -1 : 1;
}

static struct custom_operations caml_mutex_ops = {
  "_mutex",
  caml_mutex_finalize,
  caml_mutex_condition_compare,
  custom_hash_default,
  custom_serialize_default,
  custom_deserialize_default
};

value caml_mutex_new(value unit)        /* ML */
{
  pthread_mutex_t * mut;
  value wrapper;
  mut = stat_alloc(sizeof(pthread_mutex_t));
  caml_pthread_check(pthread_mutex_init(mut, NULL), "Mutex.create");
  wrapper = alloc_custom(&caml_mutex_ops, sizeof(pthread_mutex_t *),
                         1, Max_mutex_number);
  Mutex_val(wrapper) = mut;
  return wrapper;
}

value caml_mutex_lock(value wrapper)     /* ML */
{
  int retcode;
  pthread_mutex_t * mut = Mutex_val(wrapper);
  Begin_root(wrapper)           /* prevent the deallocation of mutex */
    enter_blocking_section();
    retcode = pthread_mutex_lock(mut);
    leave_blocking_section();
  End_roots();
  caml_pthread_check(retcode, "Mutex.lock");
  return Val_unit;
}

value caml_mutex_unlock(value wrapper)           /* ML */
{
  int retcode;
  pthread_mutex_t * mut = Mutex_val(wrapper);
  Begin_root(wrapper)           /* prevent the deallocation of mutex */
    enter_blocking_section();
    retcode = pthread_mutex_unlock(mut);
    leave_blocking_section();
  End_roots();
  caml_pthread_check(retcode, "Mutex.unlock");
  return Val_unit;
}

value caml_mutex_try_lock(value wrapper)           /* ML */
{
  int retcode;
  pthread_mutex_t * mut = Mutex_val(wrapper);
  retcode = pthread_mutex_trylock(mut);
  if (retcode == EBUSY) return Val_false;
  caml_pthread_check(retcode, "Mutex.try_lock");
  return Val_true;
}

/* Conditions operations */

#define Condition_val(v) (* ((pthread_cond_t **) Data_custom_val(v)))
#define Max_condition_number 1000

static void caml_condition_finalize(value wrapper)
{
  pthread_cond_t * cond = Condition_val(wrapper);
  pthread_cond_destroy(cond);
  stat_free(cond);
}

static struct custom_operations caml_condition_ops = {
  "_condition",
  caml_condition_finalize,
  caml_mutex_condition_compare,
  custom_hash_default,
  custom_serialize_default,
  custom_deserialize_default
};

value caml_condition_new(value unit)        /* ML */
{
  pthread_cond_t * cond;
  value wrapper;
  cond = stat_alloc(sizeof(pthread_cond_t));
  caml_pthread_check(pthread_cond_init(cond, NULL), "Condition.create");
  wrapper = alloc_custom(&caml_condition_ops, sizeof(pthread_cond_t *),
                         1, Max_condition_number);
  Condition_val(wrapper) = cond;
  return wrapper;
}

value caml_condition_wait(value wcond, value wmut)           /* ML */
{
  int retcode;
  pthread_cond_t * cond = Condition_val(wcond);
  pthread_mutex_t * mut = Mutex_val(wmut);
  Begin_roots2(wcond, wmut)     /* prevent deallocation of cond and mutex */
    enter_blocking_section();
    retcode = pthread_cond_wait(cond, mut);
    leave_blocking_section();
  End_roots();
  caml_pthread_check(retcode, "Condition.wait");
  return Val_unit;
}

value caml_condition_signal(value wrapper)           /* ML */
{
  int retcode;
  pthread_cond_t * cond = Condition_val(wrapper);
  Begin_root(wrapper)           /* prevent deallocation of condition */
    enter_blocking_section();
    retcode = pthread_cond_signal(cond);
    leave_blocking_section();
  End_roots();
  caml_pthread_check(retcode, "Condition.signal");
  return Val_unit;
}

value caml_condition_broadcast(value wrapper)           /* ML */
{
  int retcode;
  pthread_cond_t * cond = Condition_val(wrapper);
  Begin_root(wrapper)           /* prevent deallocation of condition */
    enter_blocking_section();
    retcode = pthread_cond_broadcast(cond);
    leave_blocking_section();
  End_roots();
  caml_pthread_check(retcode, "Condition.broadcast");
  return Val_unit;
}

/* Thread status blocks */

struct caml_threadstatus {
  pthread_mutex_t lock;          /* mutex for mutual exclusion */
  enum { ALIVE, TERMINATED } status;   /* status of thread */
  pthread_cond_t terminated;    /* signaled when thread terminates */
};

#define Threadstatus_val(v) \
  (* ((struct caml_threadstatus **) Data_custom_val(v)))
#define Max_threadstatus_number 500

static void caml_threadstatus_finalize(value wrapper)
{
  struct caml_threadstatus * ts = Threadstatus_val(wrapper);
  pthread_mutex_destroy(&ts->lock);
  pthread_cond_destroy(&ts->terminated);
  stat_free(ts);
}

static struct custom_operations caml_threadstatus_ops = {
  "_threadstatus",
  caml_threadstatus_finalize,
  caml_mutex_condition_compare,
  custom_hash_default,
  custom_serialize_default,
  custom_deserialize_default
};

value caml_threadstatus_new (void)
{
  struct caml_threadstatus * ts;
  value wrapper;
  ts = stat_alloc(sizeof(struct caml_threadstatus));
  caml_pthread_check(pthread_mutex_init(&ts->lock, NULL), "Thread.create");
  caml_pthread_check(pthread_cond_init(&ts->terminated, NULL),
                     "Thread.create");
  ts->status = ALIVE;
  wrapper = alloc_custom(&caml_threadstatus_ops,
                         sizeof(struct caml_threadstatus *),
                         1, Max_threadstatus_number);
  Threadstatus_val(wrapper) = ts;
  return wrapper;
}

void caml_threadstatus_terminate (value wrapper)
{
  struct caml_threadstatus * ts = Threadstatus_val(wrapper);
  pthread_mutex_lock(&ts->lock);
  ts->status = TERMINATED;
  pthread_mutex_unlock(&ts->lock);
  pthread_cond_broadcast(&ts->terminated);
}

int caml_threadstatus_wait (value wrapper)
{
  struct caml_threadstatus * ts = Threadstatus_val(wrapper);
  int retcode;

  Begin_roots1(wrapper)         /* prevent deallocation of ts */
    enter_blocking_section();
    retcode = pthread_mutex_lock(&ts->lock);
    if (retcode != 0) goto error;
    while (ts->status != TERMINATED) {
      retcode = pthread_cond_wait(&ts->terminated, &ts->lock);
      if (retcode != 0) goto error;
    }
    retcode = pthread_mutex_unlock(&ts->lock);
 error:
    leave_blocking_section();
  End_roots();
  return retcode;
}

/* Synchronous signal wait */

value caml_wait_signal(value sigs) /* ML */
{
  sigset_t set;
  int retcode, signo;

  sigemptyset(&set);
  while (sigs != Val_int(0)) {
    int sig = convert_signal_number(Int_val(Field(sigs, 0)));
    sigaddset(&set, sig);
    sigs = Field(sigs, 1);
  }
  enter_blocking_section();
  retcode = sigwait(&set, &signo);
  leave_blocking_section();
  caml_pthread_check(retcode, "Thread.wait_signal");
  return Val_int(signo);
}

/* Error report */

static void caml_pthread_check(int retcode, char *msg)
{
  char * err;
  int errlen, msglen;
  value str;

  if (retcode == 0) return;
  err = strerror(retcode);
  msglen = strlen(msg);
  errlen = strlen(err);
  str = alloc_string(msglen + 2 + errlen);
  memmove (&Byte(str, 0), msg, msglen);
  memmove (&Byte(str, msglen), ": ", 2);
  memmove (&Byte(str, msglen + 2), err, errlen);
  raise_sys_error(str);
}