newlib/libc/stdlib/envlock.c

   1 /*
   2 FUNCTION
   3 <<__env_lock>>, <<__env_unlock>>---lock environ variable
   4
   5 INDEX
   6         __env_lock
   7 INDEX
   8         __env_unlock
   9
  10 SYNOPSIS
  11         #include <envlock.h>
  12         void __env_lock (struct _reent *<[reent]>);
  13         void __env_unlock (struct _reent *<[reent]>);
  14
  15 DESCRIPTION
  16 The <<setenv>> family of routines call these functions when they need to
  17 modify the environ variable.  The version of these routines supplied in the
  18 library use the lock API defined in sys/lock.h.  If multiple threads of
  19 execution can call <<setenv>>, or if <<setenv>> can be called reentrantly,
  20 then you need to define your own versions of these functions in order to
  21 safely lock the memory pool during a call.  If you do not, the memory pool
  22 may become corrupted.
  23
  24 A call to <<setenv>> may call <<__env_lock>> recursively; that is,
  25 the sequence of calls may go <<__env_lock>>, <<__env_lock>>,
  26 <<__env_unlock>>, <<__env_unlock>>.  Any implementation of these
  27 routines must be careful to avoid causing a thread to wait for a lock
  28 that it already holds.
  29 */
  30
  31 #include "envlock.h"
  32 #include <sys/lock.h>
  33
  34 #ifndef __SINGLE_THREAD__
  35 __LOCK_INIT_RECURSIVE(static, __env_recursive_mutex);
  36 #endif
  37
  38 void
  39 __env_lock (ptr)
  40      struct _reent *ptr;
  41 {
  42 #ifndef __SINGLE_THREAD__
  43   __lock_acquire_recursive (__env_recursive_mutex);
  44 #endif
  45 }
  46
  47 void
  48 __env_unlock (ptr)
  49      struct _reent *ptr;
  50 {
  51 #ifndef __SINGLE_THREAD__
  52   __lock_release_recursive (__env_recursive_mutex);
  53 #endif
  54 }