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/*

 *  Author: Till Straumann <strauman@slac.stanford.edu>, 3/2002

 *

 *  envlock.c,v 1.2 2002/05/17 18:03:34 joel Exp

 */

/* provide locking for the global environment 'environ' */

#if HAVE_CONFIG_H

#include "config.h"

#endif

#include <rtems.h>

#include <sys/reent.h>

#include <assert.h>

/*

 * NOTES:

 *  - although it looks like a classical multiple-readers / single writer (MRSW)

 *    locking problem, we still use a single lock for the following reasons:

 *     1) newlib has no provision / hook for calling different locking routines

 *        from setenv/putenv and getenv, respectively.

 *     2) MRSW involves calling several semaphore-primitives, even in the most

 *        likely case of a first-reader's access. This probably takes more CPU

 *        time than just waiting until another reader is done; environment

 *        access is fast.

 *  - the lock implementation must allow nesting (same thread may call

 *    lock-lock-unlock-unlock).

 *  - NEWLIB-1.8.2 has an ugly BUG: if environ is NULL, _findenv_r() bails

 *    out leaving the lock held :-(

 *

 *  Used by the following functions:

 *    findenv_r(), setenv_r(), and unsetenv_r() which are called by

 *    getenv(), getenv_r(), setenv(), and unsetenv().

 *

 */

#if defined(ENVLOCK_DEDIDCATED_MUTEX)

static rtems_id envLock=0;

static void

__rtems_envlock_init(void)

{

  extern char        **environ;

  rtems_status_code    rc;

  if (envLock) /* already initialized */

    return;

  assert(environ && "MUST have non-NULL 'environ' due to newlib bug");

  rc = rtems_semaphore_create(

      rtems_build_name('E','N','V','S'),

      1,

      RTEMS_BINARY_SEMAPHORE | RTEMS_PRIORITY | RTEMS_INHERIT_PRIORITY,

      0,

      &envLock);

  if (RTEMS_SUCCESSFUL!=rc)

    rtems_fatal_error_occurred(rc);

}

void

__env_lock(struct _reent *r)

{

  /* Do lazy init */

  if (!envLock)

    __rtems_envlock_init();

  /*

   *  Must not use a semaphore before pre-tasking hook is called.

   *  - it will corrupt memory :-(

   */

  if (_Thread_Executing)

    rtems_semaphore_obtain(envLock, RTEMS_WAIT, RTEMS_NO_TIMEOUT);

}

void

__env_unlock(struct _reent *r)

{

  /*

   *  Must not use a semaphore before pre-tasking hook is called.

   * - it will corrupt memory :-(

   */

  if (_Thread_Executing)

    rtems_semaphore_release(envLock);

}

#else

/*

 *  Reuse the libio mutex -- it is always initialized before we

 *  could possibly run.

 */

#include <rtems/libio_.h>

void

__env_lock(struct _reent *r)

{

  rtems_semaphore_obtain( rtems_libio_semaphore, RTEMS_WAIT, RTEMS_NO_TIMEOUT );

}

void

__env_unlock(struct _reent *r)

{

  rtems_semaphore_release( rtems_libio_semaphore );

}

#endif