171 lines
4.1 KiB
ReStructuredText
171 lines
4.1 KiB
ReStructuredText
OS Data Structures
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==================
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Scalar Types
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************
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Many of the types used to communicate with NuttX are simple scalar
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types. These types are used to provide architecture independence of the
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OS from the application. The scalar types used at the NuttX interface
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include:
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.. c:type:: pid_t
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.. c:type:: size_t
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.. c:type:: sigset_t
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.. c:type:: time_t
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Hidden Interface Structures
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***************************
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Several of the types used to interface with NuttX are structures that
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are intended to be hidden from the application. From the standpoint of
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the application, these structures (and structure pointers) should be
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treated as simple handles to reference OS resources. These hidden
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structures include:
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.. c:struct:: tcb_s
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.. c:type:: mqd_t
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.. c:type:: sem_t
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.. c:type:: pthread_key_t
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In order to maintain portability, applications should not reference
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specific elements within these hidden structures. These hidden
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structures will not be described further in this user's manual.
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Access to the ``errno`` Variable
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********************************
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A pointer to the thread-specific ``errno`` value is available through a
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function call:
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.. c:function:: int *__errno(void)
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``__errno()`` returns a pointer to the thread-specific
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``errno`` value. Note that the symbol ``errno`` is defined to be
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``__errno()`` so that the usual access by referencing the symbol
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``errno`` will work as expected.
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.. code-block:: c
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#include <errno.h>
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#define errno *__errno()
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int *__errno(void);
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There is a unique, private ``errno`` value for each NuttX task. However,
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the implementation of ``errno`` differs somewhat from the use of
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``errno`` in most multi-threaded process environments: In NuttX, each
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pthread will also have its own private copy of ``errno`` and the
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``errno`` will not be shared between pthreads. This is, perhaps,
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non-standard but promotes better thread independence.
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:return: A pointer to the thread-specific ``errno`` value.
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User Interface Structures
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*************************
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.. c:type:: int (*main_t)(int argc, char *argv[])
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:c:type:`main_t` defines the type of a task entry point. :c:type:`main_t` is declared in
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``sys/types.h``.
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.. c:struct:: sched_param
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This structure is used to pass scheduling priorities to and from NuttX:
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.. code-block:: c
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struct sched_param
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{
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int sched_priority;
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};
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.. c:struct:: timespec
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This structure is used to pass timing information between the NuttX and
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a user application:
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.. code-block:: c
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struct timespec
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{
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time_t tv_sec; /* Seconds */
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long tv_nsec; /* Nanoseconds */
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};
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.. c:struct:: mq_attr
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This structure is used to communicate message queue attributes between
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NuttX and a MoBY application:
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.. code-block:: c
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struct mq_attr {
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size_t mq_maxmsg; /* Max number of messages in queue */
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size_t mq_msgsize; /* Max message size */
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unsigned mq_flags; /* Queue flags */
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size_t mq_curmsgs; /* Number of messages currently in queue */
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};
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.. note that this gives a warning due to https://github.com/sphinx-doc/sphinx/issues/7819
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.. c:struct:: sigaction
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The following structure defines the action to take for given signal:
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.. code-block:: c
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struct sigaction
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{
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union
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{
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void (*_sa_handler)(int);
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void (*_sa_sigaction)(int, siginfo_t *, void *);
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} sa_u;
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sigset_t sa_mask;
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int sa_flags;
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};
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#define sa_handler sa_u._sa_handler
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#define sa_sigaction sa_u._sa_sigaction
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.. c:struct:: siginfo
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.. c:type:: siginfo_t
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The following types is used to pass parameters to/from signal handlers:
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.. code-block:: c
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typedef struct siginfo
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{
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int si_signo;
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int si_code;
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union sigval si_value;
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} siginfo_t;
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.. c:union:: sigval
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This defines the type of the struct siginfo si_value field and is used
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to pass parameters with signals.
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.. code-block:: c
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union sigval
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{
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int sival_int;
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void *sival_ptr;
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};
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.. c:struct:: sigevent
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The following is used to attach a signal to a message queue to notify a
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task when a message is available on a queue.
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.. code-block:: c
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struct sigevent
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{
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int sigev_signo;
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union sigval sigev_value;
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int sigev_notify;
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};
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