thread.rst

Threads

Compute-intensive tasks can be offloaded from the main emulation flow with threads. Unless otherwise stated, all structures, functions and constants in this page are provided by 86box/plat.h.

Warning

86Box API functions (excluding those in this page) are generally not thread-safe and must be called from the main emulation thread. Thread-unsafe actions (such as raising an interrupt) can be performed by the callback of a free-running :doc:`timer <timer>` which looks for data written to the device's :ref:`state structure <dev/api/device:State structure>` by a thread, as timers run on the main emulation thread.

Note

The contents of thread_t and other structures used by thread_* functions are platform-specific; therefore, pointers to those structures should be treated as opaque pointers.

Starting

Threads can be started with the thread_create function. Additionally, the thread_wait function can be used to wait for a thread's function to return.

.. flat-table:: ``thread_create``
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  * - Parameter
    - Description

  * - ``thread_func``
    - Function to run in the thread. Takes the form of:

      ``void thread_func(void *priv)``

      * ``priv``: opaque pointer (see ``priv`` below).

  * - ``priv``
    - Opaque pointer passed to the ``thread_func`` above.
      Usually a pointer to a device's :ref:`state structure <dev/api/device:State structure>`.

  * - **Return value**
    - ``thread_t`` pointer representing the newly-created thread.
      That pointer will become **invalid** once the thread's function returns.

.. flat-table:: ``thread_wait``
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  * - Parameter
    - Description

  * - ``arg``
    - ``thread_t`` pointer representing the thread to wait for.

  * - **Return value**
    - * ``0`` on success;
      * Any other value on failure.

Events

Events allow for synchronization between threads. An event, represented by an event_t pointer returned by the thread_create_event function, can be set (thread_set_event function) or reset (thread_reset_event function), and a thread can wait for an event to be set with the thread_wait_event function. Events that are no longer to be used should be deallocated with the thread_destroy_event function.

.. flat-table:: ``thread_create_event``
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  * - Parameter
    - Description

  * - **Return value**
    - ``event_t`` pointer representing the newly-created event.

.. flat-table:: ``thread_set_event`` / ``thread_reset_event`` / ``thread_destroy_event``
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  * - Parameter
    - Description

  * - ``arg``
    - ``event_t`` pointer representing the event to *set* (``thread_set_event``), *reset* (``thread_reset_event``) or deallocate (``thread_destroy_event``).

.. flat-table:: ``thread_wait_event``
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  * - Parameter
    - Description

  * - ``arg``
    - ``event_t`` pointer representing the event to wait for.

  * - ``timeout``
    - Maximum amount of time in **milliseconds** (not microseconds, unlike :doc:`timers <timer>`) to spend waiting for this event to be *set*. If set to ``-1``, this function will not return until the event is *set*.

  * - **Return value**
    - * ``0`` on success;
      * Any other value if ``timeout`` was reached or the wait otherwise failed.

Note

A thread_wait_event call does not reset the event once it is set; the event must be reset manually with thread_reset_event. thread_wait_event returns immediately if the event is already set.

Mutexes

Mutexes, also known as locks, can control access to a shared resource, ensuring no concurrent modifications or other issues arise from multiple threads attempting to use the same resource at the same time. A mutex, represented by a mutex_t pointer returned by the thread_create_mutex function, can be locked with the thread_wait_mutex function (which waits until the mutex is released) and released with the thread_release_mutex function. Additionally, the status of a mutex can be independently checked with the thread_test_mutex function. Mutexes that are no longer to be used should be deallocated with the thread_close_mutex function.

.. flat-table:: ``thread_create_mutex``
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  * - Parameter
    - Description

  * - **Return value**
    - ``mutex_t`` pointer representing the newly-created mutex.

.. flat-table:: ``thread_wait_mutex`` / ``thread_release_mutex`` / ``thread_close_mutex``
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  * - Parameter
    - Description

  * - ``arg``
    - ``mutex_t`` pointer representing the mutex to *lock* (``thread_wait_mutex``), *release* (``thread_release_mutex``) or deallocate (``thread_close_mutex``).
      If this mutex is locked, ``thread_wait_mutex`` will not return until the mutex is *released* by another thread.

.. flat-table:: ``thread_test_mutex``
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  * - Parameter
    - Description

  * - ``arg``
    - ``mutex_t`` pointer representing the mutex to check.

  * - **Return value**
    - * ``0`` if this mutex is *locked*;
      * Any other value if the mutex is *released*.