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Posted 28 Sep 2002


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Win32 process suspend/resume tool

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4.68/5 (27 votes)
3 Oct 2002CPOL4 min read
A small handy command line tool for suspending/resuming the running of entire processes on Windows

Why pause and resume processes?

Anyone using the Windows NT product line (Windows 2000 and Windows XP) must have used the task manager utility. This utility, activated by pressing CTRL+SHIFT+ESC, brings up a list of the active processes and allows you several actions for controlling them: starting new processes, stopping processes and setting their priority. When you have some process that is taking a lot of resources (normally CPU time), you can easily assign it the lowest priority and the system will take care of assigning only the remaining resources or the "idle time" on the machine.

Well, a feature I always missed from Windows and present on other operating systems is the ability of pausing and resuming a process. Some daily situations you could face where this feature would be useful (actually, the ones I use it for):

  • You have a time-consuming operation, e.g. a big build, and want to pause it for doing something quickly and resuming it after doing this
  • You have some P2P software or download running and want to pause and resume it without reconnecting and want to browse some pages quickly
  • A program starts a disk trashing operation and you want to send and e-mail
  • A program starts working in a way it shouldn't for just a moment and you want to attach a debugger to it
  • You have a buggy process running and want to kill it fast

How it is done

The main problem is: there is no SuspendProcess API function. And there is no documented or safe way of doing this.

The only simple way of doing this is via SuspendThread/ResumeThread. This pair of API functions allows you to suspend and resume a thread. More than that, for the sake of safety, they maintain an internal "suspend count'. Each time you call SuspendThread, it increments this counter. ResumeThread, on the other hand, decreases this counter. If this was not done this way, the caller of SuspendThread would have no way of knowing how to restore the original state of the thread. Calling ResumeThread after calling SuspendThread effectively restores the original thread's state.

Knowing this, it is very straightforward suspending a process: it is just a matter of listing all the threads on a process, opening a handle for each of them and calling SuspendThread. The resuming is done the same way.

The ToolHelp32 API has functions for easily listing threads and processes on a system. Actually, there are two functions that do this on my code that were shamelessly borrowed from MSDN samples.

So, I wrote this little command line utility (I have an idea for integrating it with the task manager, but I have not the time for doing it right now).

How to use it

I suggest you to put the executable anywhere on the PATH. The Windows directory would be fine. Always compile this program without DLL dependencies on the CRT, so the program will start faster. You could be starting this program under very adverse conditions, so looking for a MSVCRT*.DLL and loading it could make a huge difference in the startup time.

As with most command line tools, it is meant to be used from the command prompt, by clicking on the "Command Prompt" shortcut or opening Start/Run and executing cmd.exe. The usage for the program is very simple:

pausep PID [/r]

If you type only pausep without arguments, the program will display its usage and a list of running processes and their PID. If you type pausep PID, the program will call SuspendThread on all the process's threads. This will suspend the threads or increment their suspend count. If you pass the "/r" argument, the program will do the opposite action, i.e., resuming the thread. Note that if you pausep the same process 3 times without resuming, you will need to use pausep /r it for 3 times too.

The risks with this approach

Not all programs are well written. Not all programs are made to be suspended, specially the multithreaded ones. Programs that implement timeouts may behave abnormally if you pause and resume them. When you pause and resume threads in an arbitrary order, like with this utility, you can create deadlocks.

So, only use this program when you know what you are doing.

The standard disclaimer

As I said before, this is not the safest tool in the world. Use it at your own risk: if you use it, you can loose data, profit, have hardware problems, cause radioactive contamination and start a world war. But, for me, it works fine and never had a problem.

Well, the code in this article is free for you to use any way you want. If you improve it, drop me a note, so I can keep the code in sync. If you make money with this code, you are a genius! You deserve the money. Just remember to send me a "thank you" and give me some tips. I will not reject any money you send me too.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Daniel Turini
Brazil Brazil
I develop software since I was 11. In the past 20 years, I developed software and used very different machines and languages, since Z80 based ones (ZX81, MSX) to mainframe computers. I still have passion for ASM, though no use for it anymore.
Professionally, I developed systems for managing very large databases, mainly on Sybase and SQL Server. Most of the solutions I write are for the financial market, focused on credit systems.
To date, I learned about 20 computer languages. As the moment, I'm in love with C# and the .NET framework, although I only can say I’m very proficient at C#, VB.NET(I’m not proud of this), T/SQL, C++ and libraries like ATL and STL.
I hate doing user interfaces, whether Web based or not, and I’m quite good at doing server side work and reusable components.
I’m the technical architect and one of the authors of Crivo, the most successful automated credit and risk assessment system available in Brazil.

Comments and Discussions

QuestionModify this to save the process as files, then load it later as a checkpoint Pin
JoaoXfranco20-Aug-18 7:18
MemberJoaoXfranco20-Aug-18 7:18 
NewsA much better tool Pin
Elmue29-Aug-15 4:29
MemberElmue29-Aug-15 4:29 
SuggestionEasier Approach Pin
Member 803644620-Apr-12 22:31
MemberMember 803644620-Apr-12 22:31 
GeneralThank You Pin
kazemtnt10-May-11 2:11
Memberkazemtnt10-May-11 2:11 
Generalanother api Pin
bozturk11-Jan-10 21:26
Memberbozturk11-Jan-10 21:26 
GeneralThank you! Pin
PaganBBD15-Apr-08 3:48
MemberPaganBBD15-Apr-08 3:48 
QuestionHow to query for a process's state Pin
open_mind_core27-Mar-08 8:02
Memberopen_mind_core27-Mar-08 8:02 
GeneralJust wanted to say Pin
Browner87!19-Nov-07 14:29
MemberBrowner87!19-Nov-07 14:29 
GeneralMemory Leak Pin
keremsback17-Nov-06 4:36
Memberkeremsback17-Nov-06 4:36 
GeneralProcess checkpointing Pin
Real_Jeezy5-Nov-06 4:49
MemberReal_Jeezy5-Nov-06 4:49 
GeneralI like it... Pin
Slsa749-Oct-05 9:09
MemberSlsa749-Oct-05 9:09 
GeneralToolHelp Pin
Bojan Sala3-May-05 8:27
professionalBojan Sala3-May-05 8:27 
GeneralHelp!!! Pin
jean_ni7-Apr-04 6:50
Memberjean_ni7-Apr-04 6:50 
GeneralRe: Help!!! Pin
Msftone26-Jan-06 23:11
MemberMsftone26-Jan-06 23:11 
QuestionHow to suspend/resume process on Win95? Pin
tigra_woo12-Feb-04 15:17
Membertigra_woo12-Feb-04 15:17 
AnswerRe: How to suspend/resume process on Win95? Pin
Daniel Turini13-Feb-04 0:53
MemberDaniel Turini13-Feb-04 0:53 
GeneralRe: How to suspend/resume process on Win95? Pin
tigra_woo23-Feb-04 14:53
Membertigra_woo23-Feb-04 14:53 
GeneralRe: How to suspend/resume process on Win95? Pin
Member 118805520-Jun-04 4:57
MemberMember 118805520-Jun-04 4:57 
AnswerRe: How to suspend/resume process on Win95? Pin
Member 803644620-Apr-12 22:37
MemberMember 803644620-Apr-12 22:37 
Generalaccess denied Pin
xuchangchang3-Feb-04 14:33
Memberxuchangchang3-Feb-04 14:33 
GeneralWREY was kinda right Pin
alex.barylski23-Oct-02 22:31
Memberalex.barylski23-Oct-02 22:31 
GeneralRe: WREY was kinda right Pin
*42*8-Nov-11 14:11
Member*42*8-Nov-11 14:11 
GeneralRisky, but useful too I guess Pin
Nish Nishant4-Oct-02 23:06
sitebuilderNish Nishant4-Oct-02 23:06 
GeneralDoesn't do much. Pin
WREY29-Sep-02 11:20
MemberWREY29-Sep-02 11:20 
GeneralRe: Doesn't do much. Pin
Daniel Turini29-Sep-02 12:27
MemberDaniel Turini29-Sep-02 12:27 

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