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c++windowsmultithreadingprocess
rossb83
rossb83

Reputation: 1762

Windows C++ Process vs Thread

In Windows C++, createThread() causes some of the threads to slow down if one thread is doing a very CPU intensive operation. Will createProcess() alleviate this? If so, does createProcess() imply the code must reside in a second executable, or can this all take place inside the same executable?

Upvotes: 4

Views: 5378

Answers (5)

threeapples
threeapples

Reputation: 11

Each process provides the resources needed to execute a program. A process has a virtual address space, executable code, open handles to system objects, a security context, a unique process identifier, environment variables, a priority class, minimum and maximum working set sizes, and at least one thread of execution. Each process is started with a single thread, often called the primary thread, but can create additional threads from any of its threads.

A thread is the entity within a process that can be scheduled for execution. All threads of a process share its virtual address space and system resources. In addition, each thread maintains exception handlers, a scheduling priority, thread local storage, a unique thread identifier, and a set of structures the system will use to save the thread context until it is scheduled. The thread context includes the thread's set of machine registers, the kernel stack, a thread environment block, and a user stack in the address space of the thread's process. Threads can also have their own security context, which can be used for impersonating clients.

Upvotes: 1

MSalters
MSalters

Reputation: 179819

That would make things worse. When switching threads, the CPU needs to swap out only a few registers. Since all threads of a process share the same memory, there's no need to flush the cache. But when switching betweeen processes, you also switch mapped memory. Therefore, the CPU has to flush the L1 cache. That's painful.

(L2 cache is physically mapped, i.e. uses hardware addresses. Those don't change, of course.)

Upvotes: 0

rerun
rerun

Reputation: 25505

Create process and create thread both cause additional execution on what is a resource limited environment. Meaning no matter how you do parallel processing at some point in time your other lines of execution will imped the current. It is for this reason for very large problems that are suited to parallization distributed system are used. There are pluses and minuses tho threads and processes.

Threads

Threads allow separate execution inside of one address space meaning you can share data variables instances of objects very easily, however it also means you run into many more synchronization issues. These are painfull and as you can see from the shear number of api function involved not a light subject. Threads are a lighter weight on windows then process and as such spin up and down faster and use less resources to maintain. Threads also suffer in that one thread can cause the entire process to fail.

Processes

Process each have there own address space and as such protect themselves from being brought down by another process, but lack the ability to easily communicate. Any communication will necessarily involve some type of IPC ( Pipes, TCP , ...).

The code does not have to be in a second executable just two instances need to run.

Upvotes: 0

holtavolt
holtavolt

Reputation: 4468

Not likely - a process is much "heavier" than a thread, so it is likely to be slower still. I'm not sure what you're asking about the 2nd executable, but you can use createProcess on the same .exe.

http://msdn.microsoft.com/en-us/library/ms682425(v=vs.85).aspx

It sounds like you're chasing down some performance issues, so perhaps trying out a threading-oriented profiler would be helpful: http://software.intel.com/en-us/articles/using-intel-thread-profiler-for-win32-threads-philosophy-and-theory/

Upvotes: 1

Justin Ethier
Justin Ethier

Reputation: 134157

The major difference between a process and a thread is that each process has its own memory space, while threads share the memory space of the process that they are running within.

If a thread is truly CPU bound, it will only slow another thread if they are both executing on the same processor core. createProcess will not alleviate this since a process would still have the same issue.

Also, what kind of machine are you running this on? Does it have more than one core?

Upvotes: 9

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