pthreads/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 At
  68 thread exit, if a key value has a non-NULL destructor pointer, and the
  69 thread has a non-NULL value associated with the key, the function pointed
  70 to is called with the current associated value as its sole argument.
  71 The
  72 order of destructor calls is unspecified if more than one destructor exists
  73 for a thread when it exits.
  74 .Pp
  75 If, after all the destructors have been called for all non-NULL values
  76 with associated destructors, there are still some non-NULL values with
  77 associated destructors, then the process is repeated.
  78 If, after at least
  79 [PTHREAD_DESTRUCTOR_ITERATIONS] iterations of destructor calls for
  80 outstanding non-NULL values, there are still some non-NULL values with
  81 associated destructors, the implementation stops calling destructors.
  82 .Sh RETURN VALUES
  83 If successful, the
  84 .Fn pthread_key_create
  85 function will store the newly created key value at the location specified by
  86 .Fa key
  87 and returns zero.
  88 Otherwise, an error number will be returned to indicate
  89 the error.
  90 .Sh ERRORS
  91 .Fn pthread_key_create
  92 will fail if:
  93 .Bl -tag -width Er
  94 .It Bq Er EAGAIN
  95 The system lacked the necessary resources to create another thread-specific
  96 data key, or the system-imposed limit on the total number of keys per process
  97 [PTHREAD_KEYS_MAX] would be exceeded.
  98 .It Bq Er ENOMEM
  99 Insufficient memory exists to create the key.
 100 .El
 101 .Sh SEE ALSO
 102 .Xr pthread_getspecific 3 ,
 103 .Xr pthread_key_delete 3 ,
 104 .Xr pthread_setspecific 3
 105 .Sh STANDARDS
 106 .Fn pthread_key_create
 107 conforms to
 108 .St -p1003.1-96 .