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)-文庫(kù)吧在線(xiàn)文庫(kù)
【正文】 棧的大小為8KB。 在內(nèi)核中，訪(fǎng)問(wèn)任務(wù)通常需要獲得指向其task_struct指針。3 進(jìn)程描述符的存放內(nèi)核通過(guò)一個(gè)唯一的進(jìn)程標(biāo)識(shí)值或PID來(lái)表示每個(gè)進(jìn)程。 __u32 cpu。各個(gè)進(jìn)程的task_struct存放在他們的內(nèi)核棧的尾端。在這里所說(shuō)的任務(wù)是指從內(nèi)核觀點(diǎn)看到的進(jìn)程。 通常，創(chuàng)建新的進(jìn)程都是為了立即執(zhí)行新的、不同的程序，而接著調(diào)用exec()這族函數(shù)就可以創(chuàng)建新的地址空間，并把新的程序載入。 程序本身并不是進(jìn)程：進(jìn)程是處于執(zhí)行期間的程序以及它所包含的資源的總稱(chēng)。內(nèi)核調(diào)度的對(duì)象是線(xiàn)程，而不是進(jìn)程。 The method set_current_state(state) is synonymous to set_task_state(current, state).6 Process ContextOne of the most important parts of a process is the executing program code. This code is read in from an executable file and executed within the program39。s modern RISCbased microprocessor), which stores the current task_struct in a register. Thus, current on PPC merely returns the value stored in the register r2. PPC can take this approach because, unlike x86, it has plenty of registers. Because accessing the process descriptor is a mon and important job, the PPC kernel developers deem using a register worthy for the task.4 Process StateThe state field of the process descriptor describes the current condition of the process. Each process on the system is in exactly one of five different states. This value is represented by one of five flags:(1) TASK_RUNNING The process is runnable。struct restart_block restart_block。s address space, pending signals, the process39。s state, and much more2 Allocating the Process DescriptorThe task_struct structure is allocated via the slab allocator to provide object reuse and cache coloring Prior to the kernel series, struct task_struct was stored at the end of the kernel stack of each process. This allowed architectures with few registers, such as x86, to calculate the location of the process descriptor via the stack pointer without using an extra register to store the location. With the process descriptor now dynamically created via the slab allocator, a new structure, struct thread_info, was created that again lives at the bottom of the stack and at the top of the stack . The new structure also makes it rather easy to calculate offsets of its values for use in assembly code.The thread_info structure is defined on x86 in asm/ asstruct thread_info {struct task_struct *task。unsigned long previous_esp。 it is either currently running or on a runqueue waiting to run. This is the only possible state for a process executing in userspace。s address space. Normal program execution occurs in userspace. When a program executes a system call or triggers an exception, it enters kernelspace. At this point, the kernel is said to be executing on behalf of the process and is in process context. When in process context, the current macro is valid. Upon exiting the kernel, the process resumes execution in userspace, unless a higherpriority process has bee runnable in the interim, in which case the scheduler is invoked to select the higher priority process. System calls and exception handlers are welldefined interfaces into the kernel. A process can begin executing in kernel.進(jìn)程管理進(jìn)程是Uinx操作系統(tǒng)最基本的抽象之一。在傳統(tǒng)的Unix系統(tǒng)中，一個(gè)進(jìn)程只包含一個(gè)線(xiàn)程，但現(xiàn)在的系統(tǒng)中，包含多個(gè)線(xiàn)程的多線(xiàn)程程序司空見(jiàn)慣。實(shí)際上完全可以存在兩個(gè)或者多個(gè)不同的進(jìn)程執(zhí)行的是同一個(gè)程序。在現(xiàn)代Linux內(nèi)核中，fo
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