Today, I collaborated with a vendor who executed their program through a cmd window, which logged events and activities in real-time in Windows. However, based on my past experience, accurate logs are only possible if the buffer is flushed on Windows, especially in IE. In this case, the program wrote the output to the cmd shell instead of a file. Therefore, we had to test the program and copy the logs from the window to a text file.
During testing, we encountered an issue where we couldn’t use the program because the vendor had selected text in the cmd window. The vendor claimed that running a program in this way freezes the application until the text is copied from the cmd shell.
I am uncertain if this is specific to node.js on Windows or not, as I have not heard of this before.
2 Answers
Introduction
When working with command prompt windows, it is common to encounter issues with logging real-time events. In this blog post, we will explore the concept of logging in real-time and how it can be achieved in Windows. We will also discuss the issue of freezing applications when copying text from the cmd shell and try to understand its cause.
What is Real-Time Logging?
Real-time logging refers to the ability to capture and display events as they occur, without any delay. In the context of command prompt windows, real-time logging means that any output generated by a program is immediately displayed in the cmd shell. This is in contrast to delayed logging, where the output is stored in a buffer and displayed only after a certain amount of data has accumulated.
Real-time logging is useful in situations where immediate feedback is required. For example, if a program is generating a large amount of output, it may be necessary to monitor it in real-time to ensure that it is functioning correctly.
Flushing the Buffer
As mentioned earlier, delayed logging is achieved by storing output in a buffer. In Windows, this buffer is typically 4KB in size. When the buffer is full, the data is written to the console window. However, sometimes it may be necessary to flush the buffer manually to ensure that the output is displayed immediately.
To flush the buffer, you can use the flush command. This command clears the buffer and writes any pending output to the console window. For example, if you are running a program that generates a large amount of output, you can use the following command to flush the buffer:
program.exe | flush
This will ensure that the output is displayed in real-time, rather than being delayed.
The Issue of Freezing Applications
Now, let’s turn our attention to the issue of freezing applications when copying text from the cmd shell. According to the author of the original post, running a program in the cmd shell freezes the application until after you copy the text from the cmd shell. Is this true? And if so, why?
The answer to this question lies in the way that Windows handles console applications. When a console application is launched, it is associated with a console window. This console window is where the application’s output is displayed. When you select text in the console window, Windows sends a message to the console application indicating that text has been selected.
Some console applications, such as the one mentioned in the original post, may not handle this message correctly. As a result, the application may appear to freeze until the text is copied from the console window. This is because the application is waiting for a response from Windows, but Windows is waiting for the user to complete the copy operation.
How to Prevent Freezing Applications
To prevent console applications from freezing when text is selected in the console window, you can use the SetConsoleMode function to disable mouse input. This function can be called from within a console application to modify the console input mode.
Here is an example of how to use the SetConsoleMode function to disable mouse input:
#include <windows.h>
int main()
{
HANDLE hConsoleInput = GetStdHandle(STD_INPUT_HANDLE);
DWORD dwMode = 0;
GetConsoleMode(hConsoleInput, &dwMode);
dwMode &= ~ENABLE_MOUSE_INPUT;
SetConsoleMode(hConsoleInput, dwMode);
// ... rest of program ...
}This code retrieves the console input handle, retrieves the current input mode, disables mouse input, and sets the new input mode. With mouse input disabled, the console application will not freeze when text is selected in the console window.
Conclusion
In this blog post, we have explored the concept of real-time logging in Windows command prompt windows. We have discussed the issue of delayed logging and how to flush the buffer to achieve real-time logging. We have also discussed the issue of freezing applications when text is selected in the console window and how to prevent this from happening. By understanding these concepts, you can ensure that your console applications function correctly and provide real-time feedback to the user.
If you highlight some text in the cmd.exe window, the process will continue to run in the background until it writes to the Standard Output (STDOUT) stream, which appears in the cmd.exe window. The process will resume as usual once you exit the selection mode.
You can confirm this by entering “ping www.google.com -t” in your cmd.exe window, selecting a portion of the output, and observing that it pauses. When you deselect the output, the process will resume.
It is worth noting that despite the selection, activity still occurs after the point of selection and then stops, which can be verified using a tool like Wireshark.