10.6.1 A Prolog thread for each native thread (one-to-one)
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Availability:C-language interface function
int PL_thread_attach_engine(const PL_thread_attr_t *attr)
Creates a new Prolog engine in the calling thread. If the calling thread already has an engine the reference count of the engine is incremented. The attr argument can be NULL to create a thread with default attributes. Otherwise it is a pointer to a structure as defined below. The structure must be fully initialized, including hidden fields. For any field with value‘0’, the default is used. The cancel field may be filled with a pointer to a function that is called when PL_cleanup() terminates the running Prolog engines. The function is called with the thread id (see PL_thread_self()) as argument and must return PL_THREAD_CANCEL_JOINED if the thread was reclaimed successfully, PL_THREAD_CANCEL_MUST_JOIN if the thread as cancelled, but must still be joined or PL_THREAD_CANCEL_FAILED if the request cannot be honoured. If this function is not present or returns PL_THREAD_CANCEL_FAILED pthread_cancel() is used. The new thread inherits is properties from Prolog's main thread. The flags field defines the following flags:
PL_THREAD_NO_DEBUG
If this flag is present, the thread starts in normal no-debug status. By default, the debug status is inherited from the main thread.
PL_THREAD_NOT_DETACHED
By default the new thread is created in detached mode. With this flag it is created normally, allowing Prolog to join the thread.
PL_THREAD_CUR_STREAMS
By default the current_input and current_output are set to user_input and user_output of the main thread. Using this flag, these streams are copied from the main thread. See also the inherited_from option of thread_create/3.
typedef struct
{ size_t    stack_limit;                /* Total stack limit (bytes) */
  size_t    table_space;                /* Total tabling space limit (bytes) */
  char *    alias;                      /* alias name */
  int       (*cancel)(int thread);      /* cancel function */
  intptr_t  flags;                      /* PL_THREAD_* flags */
  size_t    max_queue_size;             /* Max size of associated queue */
  char *    thread_class;               /* Class property of the thread */
} PL_thread_attr_t;

The structure may be destroyed after PL_thread_attach_engine() has returned. On success it returns the Prolog identifier for the thread (as returned by PL_thread_self()). If an error occurs, -1 is returned. If this Prolog is not compiled for multithreading, -2 is returned.