Implementation of an asynchronous file watcher with Mathematica's LibraryLink

file-watcher.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include "WolframLibrary.h"

#ifdef _WIN32
#include <windows.h>
void PortableSleep(int timems)
{
        Sleep(timems);
}
#else
#include <sys/time.h>
#include <sys/errno.h>
#include <time.h>
#include <stdlib.h>
void PortableSleep(int timems)
{
    struct timespec ts;
    ts.tv_sec = timems/1000;
    ts.tv_nsec = (timems % 1000) * 1000000;
    nanosleep(&ts, NULL);
}
#endif


typedef struct FileWatcherBackgroundArgs_st
{
    WolframIOLibrary_Functions ioLibrary;
    char *filename;
    mint pausemillis;
}* FileWatcherBackgroundArgs;

static void FileWatcherBackgroundTask(mint asyncObjID, void* vtarg)
{
    FileWatcherBackgroundArgs task_args = (FileWatcherBackgroundArgs)vtarg;
    WolframIOLibrary_Functions ioLibrary = task_args->ioLibrary;
    mint pausems = task_args->pausemillis;
    char * filename = task_args->filename;
    DataStore ds;
    free(task_args);

    while(ioLibrary->asynchronousTaskAliveQ(asyncObjID))
    {
        struct stat st = {0};
        mint time;
        int ret = lstat(filename, &st);
        if (ret == -1){
            time = -1;
        } else {
            time = (mint) st.st_mtim.tv_sec;
        }
        ds = ioLibrary->createDataStore();
        ioLibrary->DataStore_addInteger(ds, time);
        ioLibrary->raiseAsyncEvent(asyncObjID, "change", ds);
        PortableSleep((int) pausems);
    }
}

DLLEXPORT int startFileWatcher(WolframLibraryData libData, mint Argc, MArgument *Args, MArgument Res)
{
    mint asyncObjID;
    WolframIOLibrary_Functions ioLibrary = libData->ioLibraryFunctions;
    FileWatcherBackgroundArgs threadArg = (FileWatcherBackgroundArgs)malloc(sizeof(struct FileWatcherBackgroundArgs_st));
    if(Argc != 2)
        return LIBRARY_FUNCTION_ERROR;
    threadArg->ioLibrary = ioLibrary;
    threadArg->pausemillis = MArgument_getInteger(Args[0]);
    threadArg->filename = MArgument_getUTF8String(Args[1]);
    asyncObjID = ioLibrary->createAsynchronousTaskWithThread(FileWatcherBackgroundTask, threadArg);
    MArgument_setInteger(Res, asyncObjID);
    return LIBRARY_NO_ERROR;
}



/* Return the version of Library Link */
DLLEXPORT mint WolframLibrary_getVersion( ) {
	return WolframLibraryVersion;
}

/* Initialize Library */
DLLEXPORT int WolframLibrary_initialize( WolframLibraryData libData) {
	return LIBRARY_NO_ERROR;
}

/* Uninitialize Library */
DLLEXPORT void WolframLibrary_uninitialize( WolframLibraryData libData) {
	return;
}