Process and Thread Management - Windows API Reference

Processes

A process is an instance of a running program. It is an independent entity with its own virtual address space, system resources (like handles to files, devices, etc.), and security context. Each process has at least one thread of execution.

Key aspects of process management include creating new processes, terminating existing ones, and retrieving information about running processes.

Process Creation

The CreateProcess function is the primary API for creating new processes. It allows you to specify the executable to run, command-line arguments, security attributes, and other process parameters.

BOOL CreateProcess(
                        LPCTSTR lpApplicationName,
                        LPTSTR lpCommandLine,
                        LPSECURITY_ATTRIBUTES lpProcessAttributes,
                        LPSECURITY_ATTRIBUTES lpThreadAttributes,
                        BOOL bInheritHandles,
                        DWORD dwCreationFlags,
                        LPVOID lpEnvironment,
                        LPCTSTR lpCurrentDirectory,
                        LPSTARTUPINFO lpStartupInfo,
                        LPPROCESS_INFORMATION lpProcessInformation
                    );

Process Information

The PROCESS_INFORMATION structure, populated by CreateProcess, contains vital handles and identifiers for the newly created process and its primary thread. Other functions like OpenProcess and GetCurrentProcessId can be used to obtain information about existing processes.

Threads

A thread is the smallest unit of execution within a process. A process can have multiple threads, allowing for concurrent execution of tasks within the same application. Threads share the process's address space, resources, and security context.

Managing threads effectively is key to application responsiveness, especially for tasks that can be performed in parallel or in the background.

Thread Creation

The CreateThread function creates a new thread within the calling process. You specify the thread function (the entry point), arguments, and creation flags.

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

Thread Synchronization

When multiple threads access shared resources, synchronization mechanisms are essential to prevent race conditions and ensure data integrity. Common synchronization objects include:

Mutexes: Provide exclusive access to a resource.
Semaphores: Control access to a resource that can be used by a limited number of threads.
Events: Signal the occurrence of an event to one or more threads.
Critical Sections: Offer a lightweight way to synchronize access to shared data within a single process.

Key API Functions

Function	Description
`CreateProcess`	Creates a new process and its primary thread.
`CreateThread`	Creates a new thread within the calling process.
`ExitProcess`	Terminates the calling process.
`ExitThread`	Terminates the calling thread.
`OpenProcess`	Opens an existing process object.
`OpenThread`	Opens an existing thread object.
`GetCurrentProcess`	Retrieves a pseudo-handle for the current process.
`GetCurrentThread`	Retrieves a pseudo-handle for the current thread.
`WaitForSingleObject`	Waits until a specified object is in the signaled state or the time-out interval elapses.
`TerminateProcess`	Terminates an arbitrary process.
`TerminateThread`	Terminates an arbitrary thread.

Common Structures

PROCESS_INFORMATION: Contains information about a newly created process and its primary thread.
STARTUPINFO: Used by CreateProcess to specify the window station, standard handles, and appearance of the main window for the new process.
SECURITY_ATTRIBUTES: Defines the security descriptor for an object.
THREAD_START_ROUTINE: A function pointer type for the entry point of a thread.

Related Concepts

Important: Efficient process and thread management is critical for responsiveness and resource utilization. Improper synchronization can lead to deadlocks and data corruption.

Concurrency vs. Parallelism: Understanding the difference between concurrent execution (tasks making progress over time) and parallel execution (tasks running simultaneously on multiple processors).
Thread Pools: Mechanisms for efficiently managing a pool of worker threads to execute asynchronous tasks.
Job Objects: Grouping processes into a single entity for management and accounting.
Process Affinity: Controlling which CPU cores a process or thread can run on.