Process and Threads

This section provides comprehensive documentation on managing processes and threads within the Windows operating system. Understanding these concepts is crucial for developing efficient, responsive, and robust applications.

Process Management

A process is an instance of a running program. It has its own private virtual address space, system resources (like files and devices), and security context. The Windows operating system provides a rich set of APIs to create, terminate, and manage processes.

Key Concepts

• Process ID (PID): A unique identifier assigned to each running process.
• Parent Process: The process that created the current process.
• Environment Variables: Settings inherited from the parent process or system.

Core Functions

Here are some of the fundamental functions for process management:

• CreateProcess: Creates a new process and its primary thread.
• OpenProcess: Opens an existing process object.
• TerminateProcess: Terminates a process and all of its threads.
• ExitProcess: Terminates the calling process.
• GetCurrentProcess: Retrieves a pseudo-handle for the current process.
• GetProcessId: Retrieves the process identifier of the specified process.

BOOL CreateProcess(
  LPCSTR                lpApplicationName,
  LPSTR                 lpCommandLine,
  LPSECURITY_ATTRIBUTES lpProcessAttributes,
  LPSECURITY_ATTRIBUTES lpThreadAttributes,
  BOOL                  bInheritHandles,
  DWORD                 dwCreationFlags,
  LPVOID                lpEnvironment,
  LPCSTR                lpCurrentDirectory,
  LPSTARTUPINFOA        lpStartupInfo,
  LPPROCESS_INFORMATION lpProcessInformation
);

Thread Management

A thread is the basic unit of CPU utilization; it's a sequence of instructions within a process that can be executed independently. Processes can have multiple threads, allowing for concurrent execution of tasks within a single application.

Key Concepts

• Thread ID (TID): A unique identifier assigned to each thread.
• Thread States: Runnable, waiting, terminated, etc.
• Thread Synchronization: Mechanisms to coordinate access to shared resources between threads.

Core Functions

Key functions for thread management include:

• CreateThread: Creates a new thread within the calling process.
• OpenThread: Opens an existing thread object.
• TerminateThread: Terminates a thread.
• ExitThread: Terminates the calling thread.
• GetCurrentThread: Retrieves a pseudo-handle for the current thread.
• GetThreadId: Retrieves the thread identifier of the specified thread.

HANDLE CreateThread(
  LPSECURITY_ATTRIBUTES   lpThreadAttributes,
  SIZE_T                    dwStackSize,
  LPTHREAD_START_ROUTINE    lpStartAddress,
  LPVOID                    lpParameter,
  DWORD                     dwCreationFlags,
  LPDWORD                   lpThreadId
);

Interprocess Communication (IPC)

When multiple processes need to exchange data or synchronize their actions, Interprocess Communication (IPC) mechanisms are employed. Windows offers several robust IPC techniques.

IPC Mechanisms

• Pipes: Unidirectional or bidirectional data streams between processes.
• Memory-Mapped Files: Shared memory regions accessible by multiple processes.
• Sockets: Network communication endpoints for local or remote IPC.
• Message Queues: Asynchronous message passing between processes.
• Synchronization Objects: Mutexes, semaphores, events for coordinating access.

Scheduling

The Windows kernel's scheduler is responsible for allocating CPU time to threads. Developers can influence thread scheduling priorities to optimize application performance and responsiveness.

Scheduling Concepts

• Priority Levels: Threads are assigned priority levels that affect their access to the CPU.
• Time Slicing: The duration a thread runs on the CPU before potentially yielding to another thread.
• Context Switching: The process of saving the state of one thread and restoring the state of another.

Core Functions

• SetThreadPriority: Sets the priority of the specified thread.
• GetThreadPriority: Retrieves the priority of the specified thread.
• Sleep: Suspends the current thread for a specified interval.