基于arm的智能手持設(shè)備mp3播放器的設(shè)計(jì)與開(kāi)發(fā)英文參考文獻(xiàn)-全文預(yù)覽
【正文】 r_limit。unsigned long flags。s point of view.1 Process Descriptor and the Task StructureThe kernel stores the list of processes in a circular doubly linked list called the task list. Each element in the task list is a process descriptor of the type struct task_struct, which is defined in linux/.The process descriptor contains all the information about a specific process.The task_struct is a relatively large data structure, at around kilobytes on a 32bit machine. This size,however, is quite small considering that the structure contains all the information that the kernel has and needs about a process. The process descriptor contains the data that describes the executing programopen files, the process39。 a process is an active program and related resources. Indeed, two or more processes can exist that are executing the same program. In fact, two or more processes can exist that share various resources, such as open files or an address space.A process begins its life when, not surprisingly, it is created. In Linux, this occurs by means of the fork()system call, which creates a new process by duplicating an existing one. The process that calls fork() is the parent, whereas the new process is the child. The parent resumes execution and the child starts execution at the same place, where the call returns. The fork() system call returns from the kernel twice:once in the parent process and again in the newborn child.Often, immediately after a fork it is desirable to execute a new, different, program. The exec*() family of function calls is used to create a new address space and load a new program into it. In modern Linux kernels, fork() is actually implemented via the clone() system call, which is discussed in a followingsection.Finally, a program exits via the exit() system call. This function terminates the process and frees all its resources. A parent process can inquire about the status of a terminated child via the wait4() system call, which enables a process to wait for the termination of a specific process. When a process exits, it is placed into a special zombie state that is used to represent terminated processes until the parent calls wait() or waitpid().Another name for a process is a task. The Linux kernel internally refers to processes as tasks. although when I say task I am generally referring to a process from the kernel39。struct exec_domain *exec_domain。__s32 preempt_count。__u8 supervisor_stack[0]。s actual task_struct.3 Storing the Process DescriptorThe system identifies processes by a unique process identification value or PID. The PID is a numerical value that is represented by the opaque type pid_t, which is typically an int. Because of backward patibility with earlier Unix and Linux versions, however, the default maximum value is only 32,768 although the value can optionally be increased to the full range afforded the type. The kernel stores this value as pid inside each process descriptor.This maximum value is important because it is essentially the maximum number of processes that may exist concurrently on
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