mirror of https://github.com/libsdl-org/SDL
549 lines
23 KiB
C
549 lines
23 KiB
C
/*
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Simple DirectMedia Layer
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Copyright (C) 1997-2024 Sam Lantinga <slouken@libsdl.org>
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This software is provided 'as-is', without any express or implied
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warranty. In no event will the authors be held liable for any damages
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arising from the use of this software.
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Permission is granted to anyone to use this software for any purpose,
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including commercial applications, and to alter it and redistribute it
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freely, subject to the following restrictions:
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1. The origin of this software must not be misrepresented; you must not
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claim that you wrote the original software. If you use this software
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in a product, an acknowledgment in the product documentation would be
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appreciated but is not required.
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2. Altered source versions must be plainly marked as such, and must not be
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misrepresented as being the original software.
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3. This notice may not be removed or altered from any source distribution.
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*/
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/* WIKI CATEGORY: AsyncIO */
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/**
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* # CategoryAsyncIO
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*
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* SDL offers a way to perform I/O asynchronously. This allows an app to read
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* or write files without waiting for data to actually transfer; the functions
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* that request I/O never block while the request is fulfilled.
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*
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* Instead, the data moves in the background and the app can check for results
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* at their leisure.
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*
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* This is more complicated than just reading and writing files in a
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* synchronous way, but it can allow for more efficiency, and never having
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* framerate drops as the hard drive catches up, etc.
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*
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* The general usage pattern for async I/O is:
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*
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* - Create one or more SDL_AsyncIOQueue objects.
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* - Open files with SDL_AsyncIOFromFile.
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* - Start I/O tasks to the files with SDL_ReadAsyncIO or SDL_WriteAsyncIO,
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* putting those tasks into one of the queues.
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* - Later on, use SDL_GetAsyncIOResult on a queue to see if any task is
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* finished without blocking. Tasks might finish in any order with success
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* or failure.
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* - When all your tasks are done, close the file with SDL_CloseAsyncIO. This
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* also generates a task, since it might flush data to disk!
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*
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* This all works, without blocking, in a single thread, but one can also wait
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* on a queue in a background thread, sleeping until new results have arrived:
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*
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* - Call SDL_WaitAsyncIOResult from one or more threads to efficiently block
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* until new tasks complete.
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* - When shutting down, call SDL_SignalAsyncIOQueue to unblock any sleeping
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* threads despite there being no new tasks completed.
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*
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* And, of course, to match the synchronous SDL_LoadFile, we offer
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* SDL_LoadFileAsync as a convenience function. This will handle allocating a
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* buffer, slurping in the file data, and null-terminating it; you still check
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* for results later.
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*
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* Behind the scenes, SDL will use newer, efficient APIs on platforms that
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* support them: Linux's io_uring and Windows 11's IoRing, for example. If
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* those technologies aren't available, SDL will offload the work to a thread
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* pool that will manage otherwise-synchronous loads without blocking the app.
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*
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* ## Best Practices
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*
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* Simple non-blocking i/o--for an app that just wants to pick up data
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* whenever it's ready without losing framerate waiting on disks to spin--can
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* use whatever pattern works well for the program. In this case, simply call
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* SDL_ReadAsyncIO, or maybe SDL_LoadFileAsync, as needed. Once a frame, call
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* SDL_GetAsyncIOResult to check for any completed tasks and deal with the
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* data as it arrives.
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*
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* If two separate pieces of the same program need their own i/o, it is legal
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* for each to create their own queue. This will prevent either piece from
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* accidentally consuming the other's completed tasks. Each queue does require
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* some amount of resources, but it is not an overwhelming cost. Do not make a
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* queue for each task, however. It is better to put many tasks into a single
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* queue. They will be reported in order of completion, not in the order they
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* were submitted, so it doesn't generally matter what order tasks are
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* started.
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*
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* One async i/o queue can be shared by multiple threads, or one thread can
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* have more than one queue, but the most efficient way--if ruthless
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* efficiency is the goal--is to have one queue per thread, with multiple
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* threads working in parallel, and attempt to keep each queue loaded with
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* tasks that are both started by and consumed by the same thread. On modern
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* platforms that can use newer interfaces, this can keep data flowing as
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* efficiently as possible all the way from storage hardware to the app, with
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* no contention between threads for access to the same queue.
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*
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* Written data is not guaranteed to make it to physical media by the time a
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* closing task is completed, unless SDL_CloseAsyncIO is called with its
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* `flush` parameter set to true, which is to say that a successful result
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* here can still result in lost data during an unfortunately-timed power
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* outage if not flushed. However, flushing will take longer and may be
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* unnecessary, depending on the app's needs.
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*/
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#ifndef SDL_asyncio_h_
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#define SDL_asyncio_h_
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#include <SDL3/SDL_stdinc.h>
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#include <SDL3/SDL_begin_code.h>
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/* Set up for C function definitions, even when using C++ */
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#ifdef __cplusplus
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extern "C" {
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#endif
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/**
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* The asynchronous I/O operation structure.
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*
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* This operates as an opaque handle. One can then request read or write
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* operations on it.
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*
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* \since This struct is available since SDL 3.0.0.
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*
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* \sa SDL_AsyncIOFromFile
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*/
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typedef struct SDL_AsyncIO SDL_AsyncIO;
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/**
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* Types of asynchronous I/O tasks.
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*
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* \since This enum is available since SDL 3.0.0.
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*/
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typedef enum SDL_AsyncIOTaskType
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{
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SDL_ASYNCIO_TASK_READ, /**< A read operation. */
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SDL_ASYNCIO_TASK_WRITE, /**< A write operation. */
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SDL_ASYNCIO_TASK_CLOSE /**< A close operation. */
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} SDL_AsyncIOTaskType;
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/**
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* Possible outcomes of an asynchronous I/O task.
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*
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* \since This enum is available since SDL 3.0.0.
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*/
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typedef enum SDL_AsyncIOResult
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{
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SDL_ASYNCIO_COMPLETE, /**< request was completed without error */
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SDL_ASYNCIO_FAILURE, /**< request failed for some reason; check SDL_GetError()! */
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SDL_ASYNCIO_CANCELLED /**< request was cancelled before completing. */
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} SDL_AsyncIOResult;
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/**
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* Information about a completed asynchronous I/O request.
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*
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* \since This struct is available since SDL 3.0.0.
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*/
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typedef struct SDL_AsyncIOOutcome
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{
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SDL_AsyncIO *asyncio; /**< what generated this task. This pointer will be invalid if it was closed! */
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SDL_AsyncIOTaskType type; /**< What sort of task was this? Read, write, etc? */
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SDL_AsyncIOResult result; /**< the result of the work (success, failure, cancellation). */
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void *buffer; /**< buffer where data was read/written. */
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Uint64 offset; /**< offset in the SDL_AsyncIO where data was read/written. */
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Uint64 bytes_requested; /**< number of bytes the task was to read/write. */
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Uint64 bytes_transferred; /**< actual number of bytes that were read/written. */
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void *userdata; /**< pointer provided by the app when starting the task */
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} SDL_AsyncIOOutcome;
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/**
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* A queue of completed asynchronous I/O tasks.
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*
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* When starting an asynchronous operation, you specify a queue for the new
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* task. A queue can be asked later if any tasks in it have completed,
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* allowing an app to manage multiple pending tasks in one place, in whatever
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* order they complete.
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*
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* \since This struct is available since SDL 3.0.0.
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*
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* \sa SDL_CreateAsyncIOQueue
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* \sa SDL_ReadAsyncIO
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* \sa SDL_WriteAsyncIO
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* \sa SDL_GetAsyncIOResult
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* \sa SDL_WaitAsyncIOResult
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*/
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typedef struct SDL_AsyncIOQueue SDL_AsyncIOQueue;
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/**
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* Use this function to create a new SDL_AsyncIO object for reading from
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* and/or writing to a named file.
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*
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* The `mode` string understands the following values:
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*
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* - "r": Open a file for reading only. It must exist.
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* - "w": Open a file for writing only. It will create missing files or
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* truncate existing ones.
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* - "r+": Open a file for update both reading and writing. The file must
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* exist.
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* - "w+": Create an empty file for both reading and writing. If a file with
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* the same name already exists its content is erased and the file is
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* treated as a new empty file.
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*
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* There is no "b" mode, as there is only "binary" style I/O, and no "a" mode
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* for appending, since you specify the position when starting a task.
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*
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* This function supports Unicode filenames, but they must be encoded in UTF-8
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* format, regardless of the underlying operating system.
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*
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* This call is _not_ asynchronous; it will open the file before returning,
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* under the assumption that doing so is generally a fast operation. Future
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* reads and writes to the opened file will be async, however.
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*
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* \param file a UTF-8 string representing the filename to open.
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* \param mode an ASCII string representing the mode to be used for opening
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* the file.
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* \returns a pointer to the SDL_AsyncIO structure that is created or NULL on
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* failure; call SDL_GetError() for more information.
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*
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* \since This function is available since SDL 3.2.0.
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*
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* \sa SDL_CloseAsyncIO
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* \sa SDL_ReadAsyncIO
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* \sa SDL_WriteAsyncIO
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*/
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extern SDL_DECLSPEC SDL_AsyncIO * SDLCALL SDL_AsyncIOFromFile(const char *file, const char *mode);
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/**
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* Use this function to get the size of the data stream in an SDL_AsyncIO.
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*
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* This call is _not_ asynchronous; it assumes that obtaining this info is a
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* non-blocking operation in most reasonable cases.
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*
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* \param asyncio the SDL_AsyncIO to get the size of the data stream from.
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* \returns the size of the data stream in the SDL_IOStream on success or a
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* negative error code on failure; call SDL_GetError() for more
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* information.
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*
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* \threadsafety It is safe to call this function from any thread.
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*
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* \since This function is available since SDL 3.2.0.
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*/
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extern SDL_DECLSPEC Sint64 SDLCALL SDL_GetAsyncIOSize(SDL_AsyncIO *asyncio);
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/**
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* Start an async read.
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*
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* This function reads up to `size` bytes from `offset` position in the data
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* source to the area pointed at by `ptr`. This function may read less bytes
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* than requested.
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*
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* This function returns as quickly as possible; it does not wait for the read
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* to complete. On a successful return, this work will continue in the
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* background. If the work begins, even failure is asynchronous: a failing
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* return value from this function only means the work couldn't start at all.
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*
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* `ptr` must remain available until the work is done, and may be accessed by
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* the system at any time until then. Do not allocate it on the stack, as this
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* might take longer than the life of the calling function to complete!
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*
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* An SDL_AsyncIOQueue must be specified. The newly-created task will be added
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* to it when it completes its work.
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*
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* \param asyncio a pointer to an SDL_AsyncIO structure.
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* \param ptr a pointer to a buffer to read data into.
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* \param offset the position to start reading in the data source.
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* \param size the number of bytes to read from the data source.
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* \param queue a queue to add the new SDL_AsyncIO to.
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* \param userdata an app-defined pointer that will be provided with the task
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* results.
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* \returns true on success or false on failure; call SDL_GetError() for more
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* information.
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*
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* \threadsafety It is safe to call this function from any thread.
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*
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* \since This function is available since SDL 3.2.0.
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*
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* \sa SDL_WriteAsyncIO
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* \sa SDL_CreateAsyncIOQueue
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* \sa SDL_GetAsyncIOTaskResult
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*/
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extern SDL_DECLSPEC bool SDLCALL SDL_ReadAsyncIO(SDL_AsyncIO *asyncio, void *ptr, Uint64 offset, Uint64 size, SDL_AsyncIOQueue *queue, void *userdata);
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/**
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* Start an async write.
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*
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* This function writes `size` bytes from `offset` position in the data source
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* to the area pointed at by `ptr`.
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*
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* This function returns as quickly as possible; it does not wait for the
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* write to complete. On a successful return, this work will continue in the
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* background. If the work begins, even failure is asynchronous: a failing
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* return value from this function only means the work couldn't start at all.
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*
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* `ptr` must remain available until the work is done, and may be accessed by
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* the system at any time until then. Do not allocate it on the stack, as this
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* might take longer than the life of the calling function to complete!
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*
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* An SDL_AsyncIOQueue must be specified. The newly-created task will be added
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* to it when it completes its work.
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*
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* \param asyncio a pointer to an SDL_AsyncIO structure.
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* \param ptr a pointer to a buffer to write data from.
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* \param offset the position to start writing to the data source.
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* \param size the number of bytes to write to the data source.
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* \param queue a queue to add the new SDL_AsyncIO to.
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* \param userdata an app-defined pointer that will be provided with the task
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* results.
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* \returns true on success or false on failure; call SDL_GetError() for more
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* information.
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*
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* \threadsafety It is safe to call this function from any thread.
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*
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* \since This function is available since SDL 3.2.0.
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*
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* \sa SDL_ReadAsyncIO
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* \sa SDL_CreateAsyncIOQueue
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* \sa SDL_GetAsyncIOTaskResult
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*/
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extern SDL_DECLSPEC bool SDLCALL SDL_WriteAsyncIO(SDL_AsyncIO *asyncio, void *ptr, Uint64 offset, Uint64 size, SDL_AsyncIOQueue *queue, void *userdata);
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/**
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* Close and free any allocated resources for an async I/O object.
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*
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* Closing a file is _also_ an asynchronous task! If a write failure were to
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* happen during the closing process, for example, the task results will
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* report it as usual.
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*
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* Closing a file that has been written to does not guarantee the data has
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* made it to physical media; it may remain in the operating system's file
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* cache, for later writing to disk. This means that a successfully-closed
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* file can be lost if the system crashes or loses power in this small window.
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* To prevent this, call this function with the `flush` parameter set to true.
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* This will make the operation take longer, and perhaps increase system load
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* in general, but a successful result guarantees that the data has made it to
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* physical storage. Don't use this for temporary files, caches, and
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* unimportant data, and definitely use it for crucial irreplaceable files,
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* like game saves.
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*
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* This function guarantees that the close will happen after any other pending
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* tasks to `asyncio`, so it's safe to open a file, start several operations,
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* close the file immediately, then check for all results later. This function
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* will not block until the tasks have completed.
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*
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* Once this function returns non-NULL, `asyncio` is no longer valid,
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* regardless of any future outcomes. Any completed tasks might still contain
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* this pointer in their SDL_AsyncIOOutcome data, in case the app was using
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* this value to track information, but it should not be used again.
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*
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* If this function returns false, the close wasn't started at all, and it's
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* safe to attempt to close again later.
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*
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* An SDL_AsyncIOQueue must be specified. The newly-created task will be added
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* to it when it completes its work.
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*
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* \param asyncio a pointer to an SDL_AsyncIO structure to close.
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* \param flush true if data should sync to disk before the task completes.
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* \param queue a queue to add the new SDL_AsyncIO to.
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* \param userdata an app-defined pointer that will be provided with the task
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* results.
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* \returns true on success or false on failure; call SDL_GetError() for more
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* information.
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*
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* \threadsafety It is safe to call this function from any thread, but two
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* threads should not attempt to close the same object.
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*
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* \since This function is available since SDL 3.2.0.
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*/
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extern SDL_DECLSPEC bool SDLCALL SDL_CloseAsyncIO(SDL_AsyncIO *asyncio, bool flush, SDL_AsyncIOQueue *queue, void *userdata);
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/**
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* Create a task queue for tracking multiple I/O operations.
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*
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* Async I/O operations are assigned to a queue when started. The queue can be
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* checked for completed tasks thereafter.
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*
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* \returns a new task queue object or NULL if there was an error; call
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* SDL_GetError() for more information.
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*
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* \threadsafety It is safe to call this function from any thread.
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*
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* \since This function is available since SDL 3.2.0.
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*
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* \sa SDL_DestroyAsyncIOQueue
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* \sa SDL_GetAsyncIOResult
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* \sa SDL_WaitAsyncIOResult
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*/
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extern SDL_DECLSPEC SDL_AsyncIOQueue * SDLCALL SDL_CreateAsyncIOQueue(void);
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/**
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* Destroy a previously-created async I/O task queue.
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*
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* If there are still tasks pending for this queue, this call will block until
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* those tasks are finished. All those tasks will be deallocated. Their
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* results will be lost to the app.
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*
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* Any pending reads from SDL_LoadFileAsync() that are still in this queue
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* will have their buffers deallocated by this function, to prevent a memory
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* leak.
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*
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* Once this function is called, the queue is no longer valid and should not
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* be used, including by other threads that might access it while destruction
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* is blocking on pending tasks.
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*
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* Do not destroy a queue that still has threads waiting on it through
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* SDL_WaitAsyncIOResult(). You can call SDL_SignalAsyncIOQueue() first to
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* unblock those threads, and take measures (such as SDL_WaitThread()) to make
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* sure they have finished their wait and won't wait on the queue again.
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*
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* \param queue the task queue to destroy.
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*
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* \threadsafety It is safe to call this function from any thread, so long as
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* no other thread is waiting on the queue with
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* SDL_WaitAsyncIOResult.
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*
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* \since This function is available since SDL 3.2.0.
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*/
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extern SDL_DECLSPEC void SDLCALL SDL_DestroyAsyncIOQueue(SDL_AsyncIOQueue *queue);
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/**
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* Query an async I/O task queue for completed tasks.
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*
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* If a task assigned to this queue has finished, this will return true and
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* fill in `outcome` with the details of the task. If no task in the queue has
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* finished, this function will return false. This function does not block.
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*
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* If a task has completed, this function will free its resources and the task
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* pointer will no longer be valid. The task will be removed from the queue.
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*
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* It is safe for multiple threads to call this function on the same queue at
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* once; a completed task will only go to one of the threads.
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*
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* \param queue the async I/O task queue to query.
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* \param outcome details of a finished task will be written here. May not be
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* NULL.
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* \returns true if task has completed, false otherwise.
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*
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* \threadsafety It is safe to call this function from any thread.
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*
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* \since This function is available since SDL 3.2.0.
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*
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* \sa SDL_WaitAsyncIOResult
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*/
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extern SDL_DECLSPEC bool SDLCALL SDL_GetAsyncIOResult(SDL_AsyncIOQueue *queue, SDL_AsyncIOOutcome *outcome);
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/**
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* Block until an async I/O task queue has a completed task.
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*
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* This function puts the calling thread to sleep until there a task assigned
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* to the queue that has finished.
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*
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* If a task assigned to the queue has finished, this will return true and
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* fill in `outcome` with the details of the task. If no task in the queue has
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* finished, this function will return false.
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*
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* If a task has completed, this function will free its resources and the task
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|
* pointer will no longer be valid. The task will be removed from the queue.
|
|
*
|
|
* It is safe for multiple threads to call this function on the same queue at
|
|
* once; a completed task will only go to one of the threads.
|
|
*
|
|
* Note that by the nature of various platforms, more than one waiting thread
|
|
* may wake to handle a single task, but only one will obtain it, so
|
|
* `timeoutMS` is a _maximum_ wait time, and this function may return false
|
|
* sooner.
|
|
*
|
|
* This function may return false if there was a system error, the OS
|
|
* inadvertently awoke multiple threads, or if SDL_SignalAsyncIOQueue() was
|
|
* called to wake up all waiting threads without a finished task.
|
|
*
|
|
* A timeout can be used to specify a maximum wait time, but rather than
|
|
* polling, it is possible to have a timeout of -1 to wait forever, and use
|
|
* SDL_SignalAsyncIOQueue() to wake up the waiting threads later.
|
|
*
|
|
* \param queue the async I/O task queue to wait on.
|
|
* \param outcome details of a finished task will be written here. May not be
|
|
* NULL.
|
|
* \param timeoutMS the maximum time to wait, in milliseconds, or -1 to wait
|
|
* indefinitely.
|
|
* \returns true if task has completed, false otherwise.
|
|
*
|
|
* \threadsafety It is safe to call this function from any thread.
|
|
*
|
|
* \since This function is available since SDL 3.2.0.
|
|
*
|
|
* \sa SDL_SignalAsyncIOQueue
|
|
*/
|
|
extern SDL_DECLSPEC bool SDLCALL SDL_WaitAsyncIOResult(SDL_AsyncIOQueue *queue, SDL_AsyncIOOutcome *outcome, Sint32 timeoutMS);
|
|
|
|
/**
|
|
* Wake up any threads that are blocking in SDL_WaitAsyncIOResult().
|
|
*
|
|
* This will unblock any threads that are sleeping in a call to
|
|
* SDL_WaitAsyncIOResult for the specified queue, and cause them to return
|
|
* from that function.
|
|
*
|
|
* This can be useful when destroying a queue to make sure nothing is touching
|
|
* it indefinitely. In this case, once this call completes, the caller should
|
|
* take measures to make sure any previously-blocked threads have returned
|
|
* from their wait and will not touch the queue again (perhaps by setting a
|
|
* flag to tell the threads to terminate and then using SDL_WaitThread() to
|
|
* make sure they've done so).
|
|
*
|
|
* \param queue the async I/O task queue to signal.
|
|
*
|
|
* \threadsafety It is safe to call this function from any thread.
|
|
*
|
|
* \since This function is available since SDL 3.2.0.
|
|
*
|
|
* \sa SDL_WaitAsyncIOResult
|
|
*/
|
|
extern SDL_DECLSPEC void SDLCALL SDL_SignalAsyncIOQueue(SDL_AsyncIOQueue *queue);
|
|
|
|
/**
|
|
* Load all the data from a file path, asynchronously.
|
|
*
|
|
* This function returns as quickly as possible; it does not wait for the read
|
|
* to complete. On a successful return, this work will continue in the
|
|
* background. If the work begins, even failure is asynchronous: a failing
|
|
* return value from this function only means the work couldn't start at all.
|
|
*
|
|
* The data is allocated with a zero byte at the end (null terminated) for
|
|
* convenience. This extra byte is not included in SDL_AsyncIOOutcome's
|
|
* bytes_transferred value.
|
|
*
|
|
* This function will allocate the buffer to contain the file. It must be
|
|
* deallocated by calling SDL_free() on SDL_AsyncIOOutcome's buffer field
|
|
* after completion.
|
|
*
|
|
* An SDL_AsyncIOQueue must be specified. The newly-created task will be added
|
|
* to it when it completes its work.
|
|
*
|
|
* \param file the path to read all available data from.
|
|
* \param queue a queue to add the new SDL_AsyncIO to.
|
|
* \param userdata an app-defined pointer that will be provided with the task
|
|
* results.
|
|
* \returns true on success or false on failure; call SDL_GetError() for more
|
|
* information.
|
|
*
|
|
* \since This function is available since SDL 3.2.0.
|
|
*
|
|
* \sa SDL_LoadFile_IO
|
|
*/
|
|
extern SDL_DECLSPEC bool SDLCALL SDL_LoadFileAsync(const char *file, SDL_AsyncIOQueue *queue, void *userdata);
|
|
|
|
/* Ends C function definitions when using C++ */
|
|
#ifdef __cplusplus
|
|
}
|
|
#endif
|
|
#include <SDL3/SDL_close_code.h>
|
|
|
|
#endif /* SDL_asyncio_h_ */
|