man/pthread_key_create.3

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  33 .Dd April 4, 1996
  34 .Dt PTHREAD_KEY_CREATE 3
  35 .Os
  36 .Sh NAME
  37 .Nm pthread_key_create
  38 .Nd thread-specific data key creation
  39 .Sh SYNOPSIS
  40 .Fd #include <pthread.h>
  41 .Ft int
  42 .Fo pthread_key_create
  43 .Fa "pthread_key_t *key"
  44 .Fa "void (*destructor)(void *)"
  45 .Fc
  46 .Sh DESCRIPTION
  47 The
  48 .Fn pthread_key_create
  49 function creates a thread-specific data key
  50 that is visible to all threads in the process.
  51 Key values provided by
  52 .Fn pthread_key_create
  53 are opaque objects, used to locate thread-specific data.
  54 Although the same
  55 key value may be used by different threads, the values bound to the key
  56 by
  57 .Fn pthread_setspecific
  58 are maintained on a per-thread basis and persist for the life of the calling
  59 thread.
  60 .Pp
  61 Upon key creation, the value NULL is associated with the new key in all
  62 active threads.
  63 Upon thread creation, the value NULL is associated with all
  64 defined keys in the new thread.
  65 .Pp
  66 An optional destructor function may be associated with each key value.
  67 If a key value has a non-NULL destructor function pointer, and the thread has
  68 a non-NULL value associated with the key at the time of thread exit, then the
  69 key value is set to NULL and the destructor function is called with the
  70 previous key value as its argument.
  71 The order of destructor calls at thread exit is unspecified.
  72 .Pp
  73 If, after all the destructors have been called for all non-NULL values
  74 with associated destructors, there are still some non-NULL values with
  75 associated destructors, then the process is repeated.
  76 If, after at least
  77 [PTHREAD_DESTRUCTOR_ITERATIONS] iterations of destructor calls for
  78 outstanding non-NULL values, there are still some non-NULL values with
  79 associated destructors, the implementation stops calling destructors.
  80 .Sh RETURN VALUES
  81 If successful, the
  82 .Fn pthread_key_create
  83 function will store the newly created key value at the location specified by
  84 .Fa key
  85 and returns zero.
  86 Otherwise, an error number will be returned to indicate
  87 the error.
  88 .Sh ERRORS
  89 .Fn pthread_key_create
  90 will fail if:
  91 .Bl -tag -width Er
  92 .It Bq Er EAGAIN
  93 The system lacked the necessary resources to create another thread-specific
  94 data key, or the system-imposed limit on the total number of keys per process
  95 [PTHREAD_KEYS_MAX] would be exceeded.
  96 .It Bq Er ENOMEM
  97 Insufficient memory exists to create the key.
  98 .El
  99 .Sh SEE ALSO
 100 .Xr pthread_getspecific 3 ,
 101 .Xr pthread_key_delete 3 ,
 102 .Xr pthread_setspecific 3
 103 .Sh STANDARDS
 104 .Fn pthread_key_create
 105 conforms to
 106 .St -p1003.1-96 .