Multiple file modified events fired per file save

[richardeakin]

Hi,

I'm testing out this nice library in an UE4 setting and noticing that while it is working quite well for add and remove, modified is firing twice whenever I update a file (save it in a text editor). Is this a known thing, or is there some way I can avoid it?

Also, when I add a new file to my watched directory, I see two events: one add and one modified - perhaps this is a hint to the problem. Here is the code I'm testing with in a C++ Actor. Note I'm also printing the current frame, which is sometimes the same for the redundant modified event, sometimes it is a frame later.

// Fill out your copyright notice in the Description page of Project Settings.


#include "FileMonitorTest.h"
#include "./FileWatch.hpp"
#include <string>

#define PRINT_DISPLAY_TIME 3.0f
#define printf(format, ...)                 if (GEngine) GEngine->AddOnScreenDebugMessage(-1, PRINT_DISPLAY_TIME, FColor::White, FString::Printf(TEXT(format), ##__VA_ARGS__), false)

// Sets default values
AFileMonitorTest::AFileMonitorTest()
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;

}

namespace {
const char* watchEventTypeToString( const filewatch::Event change_type )
{
	switch (change_type) {
		case filewatch::Event::added:			return "added";
		case filewatch::Event::removed:			return "removed";
		case filewatch::Event::modified:		return "modified";
		case filewatch::Event::renamed_old:		return "renamed_old";
		case filewatch::Event::renamed_new:		return "renamed_new";
		default: break;
	};

	return "(unknown)";
}
}

// Called when the game starts or when spawned
void AFileMonitorTest::BeginPlay()
{
	Super::BeginPlay();
	
	// we'll add a watcher for file changes in this directory
	std::wstring scanDir( L"E:/epic/Unreal Projects/FileMonitoring/data/scans" );

	IPlatformFile& PlatformFile = FPlatformFileManager::Get().GetPlatformFile();
	bool dirExists = PlatformFile.DirectoryExists(scanDir.c_str());
	printf("scanDir: %s, exists: %d", scanDir.c_str(), dirExists );

	if( dirExists ) {
		// print out contents of folder using ue4 stuffs
		TArray<FString> fileNames;
		PlatformFile.FindFiles( fileNames, scanDir.c_str(), NULL );
		printf("num files: %d", fileNames.Num() );
		for( int i = 0; i < fileNames.Num(); i++ ) {
			printf( "%s", *fileNames[i] );
		}

		// watch for file changes within scanDir
		static filewatch::FileWatch<std::wstring> watch(
			scanDir, 
			[](const std::wstring& path, const filewatch::Event change_type ) {
				FString changeTypeStr = watchEventTypeToString( change_type );using char* directly prints rubbish
				printf("path: %s, event type: %s, frame: %d", path.c_str(), *changeTypeStr, GFrameNumber );
			}
		);
	}
}

// Called every frame
void AFileMonitorTest::Tick(float DeltaTime)
{
	Super::Tick(DeltaTime);

}

[richardeakin]

Another interesting note: if I hit save one an empty file, then I only get one modified event fired. But if it has contents, then I get two modified events fired.

[deadash]

I also have this problem in windows, if I delete and write it is removed\added\modified.
If it is modified directly, it is modified twice.

[deadash]

There seems to be no good way to solve this problem

Most people use the anti-shake function call, or view the last modification time of the file.

You can use procmon to check the occurrence of the event, it should also be twice.

https://stackoverflow.com/questions/1764809/filesystemwatcher-changed-event-is-raised-twice
https://stackoverflow.com/questions/14036449/c-winapi-readdirectorychangesw-receiving-double-notifications