LIBJXL
Macros | Typedefs
parallel_runner.h File Reference
#include <stddef.h>
#include <stdint.h>
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Macros

#define JXL_PARALLEL_RET_RUNNER_ERROR   (-1)
 

Typedefs

typedef int JxlParallelRetCode
 
typedef JxlParallelRetCode(* JxlParallelRunInit) (void *jpegxl_opaque, size_t num_threads)
 
typedef void(* JxlParallelRunFunction) (void *jpegxl_opaque, uint32_t value, size_t thread_id)
 
typedef JxlParallelRetCode(* JxlParallelRunner) (void *runner_opaque, void *jpegxl_opaque, JxlParallelRunInit init, JxlParallelRunFunction func, uint32_t start_range, uint32_t end_range)
 

Macro Definition Documentation

◆ JXL_PARALLEL_RET_RUNNER_ERROR

#define JXL_PARALLEL_RET_RUNNER_ERROR   (-1)

General error returned by the JxlParallelRunInit function to indicate an error.

Typedef Documentation

◆ JxlParallelRetCode

typedef int JxlParallelRetCode

API for running data operations in parallel in a multi-threaded environment. This module allows the JPEG XL caller to define their own way of creating and assigning threads.

The JxlParallelRunner function type defines a parallel data processing runner that may be implemented by the caller to allow the library to process in multiple threads. The multi-threaded processing in this library only requires to run the same function over each number of a range, possibly running each call in a different thread. The JPEG XL caller is responsible for implementing this logic using the thread APIs available in their system. For convenience, a C++ implementation based on std::thread is provided in jpegxl/parallel_runner_thread.h (part of the jpegxl_threads library).

Thread pools usually store small numbers of heterogeneous tasks in a queue. When tasks are identical or differ only by an integer input parameter, it is much faster to store just one function of an integer parameter and call it for each value. Conventional vector-of-tasks can be run in parallel using a lambda function adapter that simply calls task_funcs[task].

If no multi-threading is desired, a NULL value of JxlParallelRunner will use an internal implementation without multi-threading. Return code used in the JxlParallel* functions as return value. A value of 0 means success and any other value means error. The special value JXL_PARALLEL_RET_RUNNER_ERROR can be used by the runner to indicate any other error.

◆ JxlParallelRunFunction

typedef void(* JxlParallelRunFunction) (void *jpegxl_opaque, uint32_t value, size_t thread_id)

Parallel run data processing callback. See JxlParallelRunner for details.

This function MUST be called once for every number in the range [start_range, end_range) (including start_range but not including end_range) passing this number as the value. Calls for different value may be executed from different threads in parallel.

Parameters
jpegxl_opaquethe jpegxl_opaque handle provided to JxlParallelRunner() must be passed here.
valuethe number in the range [start_range, end_range) of the call.
thread_idthe thread number where this function is being called from. This must be lower than the num_threads value passed to JxlParallelRunInit.

◆ JxlParallelRunInit

typedef JxlParallelRetCode(* JxlParallelRunInit) (void *jpegxl_opaque, size_t num_threads)

Parallel run initialization callback. See JxlParallelRunner for details.

This function MUST be called by the JxlParallelRunner only once, on the same thread that called JxlParallelRunner, before any parallel execution. The purpose of this call is to provide the maximum number of threads that the JxlParallelRunner will use, which can be used by JPEG XL to allocate per-thread storage if needed.

Parameters
jpegxl_opaquethe jpegxl_opaque handle provided to JxlParallelRunner() must be passed here.
num_threadsthe maximum number of threads. This value must be positive.
Returns
0 if the initialization process was successful.
an error code if there was an error, which should be returned by JxlParallelRunner().

◆ JxlParallelRunner

typedef JxlParallelRetCode(* JxlParallelRunner) (void *runner_opaque, void *jpegxl_opaque, JxlParallelRunInit init, JxlParallelRunFunction func, uint32_t start_range, uint32_t end_range)

JxlParallelRunner function type. A parallel runner implementation can be provided by a JPEG XL caller to allow running computations in multiple threads. This function must call the initialization function init in the same thread that called it and then call the passed func once for every number in the range [start_range, end_range) (including start_range but not including end_range) possibly from different multiple threads in parallel.

The JxlParallelRunner function does not need to be re-entrant. This means that the same JxlParallelRunner function with the same runner_opaque provided parameter will not be called from the library from either init or func in the same decoder or encoder instance. However, a single decoding or encoding instance may call the provided JxlParallelRunner multiple times for different parts of the decoding or encoding process.

Returns
0 if the init call succeeded (returned 0) and no other error occurred in the runner code.
JXL_PARALLEL_RET_RUNNER_ERROR if an error occurred in the runner code, for example, setting up the threads.
the return value of init() if non-zero.