本文共 18402 字,大约阅读时间需要 61 分钟。
以下摘自百度百科:
进程(Process)是计算机中的程序关于某数据集合上的一次运行活动,是系统进行资源分配和调度的基本单位,是操作系统结构的基础。在早期面向进程设计的计算机结构中,进程是程序的基本执行实体;在当代面向线程设计的计算机结构中,进程是线程的容器。程序是指令、数据及其组织形式的描述,进程是程序的实体
当然,上述只是宏观概念上的抽象描述,我们在本科学习操作系统时,一般老师最喜欢讲这种。那么,进程在操作系统中真正意义上是怎么表示的呢?
我分析的源码版本:linux-2.6.34
linux内核通过task_struct(进程描述符)结构体来管理进程,这个结构体包含了一个进程所需的所有信息。它定义在linux-2.6.34\include\linux\sched.h文件中
关于进程状态,源码中的注释如下:
/*
* Task state bitmask. NOTE! These bits are also * encoded in fs/proc/array.c: get_task_state(). * * We have two separate sets of flags: task->state * is about runnability, while task->exit_state are * about the task exiting. Confusing, but this way * modifying one set can't modify the other one by * mistake. */进程状态分为两类:struct_task中成员state(关于运行的状态)和exit_state(关于退出的状态)
#define TASK_RUNNING 0#define TASK_INTERRUPTIBLE 1#define TASK_UNINTERRUPTIBLE 2#define __TASK_STOPPED 4#define __TASK_TRACED 8/* in tsk->exit_state */#define EXIT_ZOMBIE 16#define EXIT_DEAD 32/* in tsk->state again */#define TASK_DEAD 64#define TASK_WAKEKILL 128#define TASK_WAKING 256#define TASK_STATE_MAX 512
TASK_RUNNING:表示进程要么正在执行,要么正要准备执行
处于这种状态的进程,要么正在运行、要么正准备运行。正在运行的进程就是当前进程(由current所指向的进程),而准备运行的进程只要得到CPU就可以立即投入运行,CPU是这些进程唯一等待的系统资源。系统中有一个运行队列(run_queue),用来容纳所有处于可运行状态的进程,调度程序执行时,从中选择一个进程投入运行。在后面我们讨论进程调度的时候,可以看到运行队列的作用。当前运行进程一直处于该队列中,也就是说,current总是指向运行队列中的某个元素,只是具体指向谁由调度程序决定。
TASK_INTERRUPTIBLE:E表示进程被阻塞(睡眠),直到某个条件变为真。条件一旦达成,进程的状态就被设置为TASK_RUNNING。
处于该状态的进程正在等待某个事件(event)或某个资源,它肯定位于系统中的某个等待队列(wait_queue)中。Linux中处于等待状态的进程分为两种:可中断的等待状态和不可中断的等待状态。处于可中断等待态的进程可以被信号唤醒,如果收到信号,该进程就从等待状态进入可运行状态,并且加入到运行队列中,等待被调度;而处于不可中断等待态的进程是因为硬件环境不能满足而等待,例如等待特定的系统资源,它任何情况下都不能被打断,只能用特定的方式来唤醒它,例如唤醒函数wake_up()等。
TASK_UNINTERRUPTIBLE:TASK_UNINTERRUPTIBLE的意义与TASK_INTERRUPTIBLE类似,除了不能通过接受一个信号来唤醒
__TASK_STOPPED:表示进程被停止执行
此时的进程暂时停止运行来接受某种特殊处理。通常当进程接收到SIGSTOP、SIGTSTP、SIGTTIN或 SIGTTOU信号后就处于这种状态。例如,正接受调试的进程就处于这种状态。
__TASK_TRACED:表示进程被debugger等进程监视
/* exit_state */EXIT_ZOMBIE:表示进程的执行被终止,但是其父进程还没有使用wait()等系统调用来获知它的终止信息
进程虽然已经终止,但由于某种原因,父进程还没有执行wait()等系统调用,终止进程的信息也还没有回收。顾名思义,处于该状态的进程就是僵尸进程,这种进程实际上是系统中的垃圾,必须进行相应处理以释放其占用的资源。
EXIT_DEAD:表示进程的最终状态
具体参见我的另一篇博文 http://blog.csdn.net/tiankong_/article/details/75647488
什么是进程的内核栈? 进程在内核态运行时需要自己的堆栈信息, 因此linux内核为每个进程都提供了一个内核栈kernel stackvoid *stack;task_struct数据结构中的stack成员指向 thread_union结构(Linux内核通过thread_union联合体来表示进程的内核栈) 内核栈的大小? 进程通过alloc_thread_info函数分配它的内核栈,通过free_thread_info函数释放所分配的内核栈,查看源码 alloc_thread_info函数通过调用__get_free_pages函数分配2个页的内存(8192字节)
/* * pointers to (original) parent process, youngest child, younger sibling, * older sibling, respectively. (p->father can be replaced with * p->real_parent->pid) */ struct task_struct *real_parent; /* real parent process */ struct task_struct *parent; /* recipient of SIGCHLD, wait4() reports */ /* * children/sibling forms the list of my natural children */ struct list_head children; /* list of my children */ struct list_head sibling; /* linkage in my parent's children list */ struct task_struct *group_leader; /* threadgroup leader */real_parent:指向其父进程,如果创建它的父进程不再存在,则指向PID为1的init进程
parent:指向其父进程,当它终止时,必须向它的父进程发送信号。它的值通常与real_parent相同
children:指向子进程链表
sibling:指向兄弟链表
group_leader:指向其所在进程组的领头进程
unsigned int flags;
flags成员的可能取值如下:
#define PF_KSOFTIRQD 0x00000001 /* I am ksoftirqd */ #define PF_STARTING 0x00000002 /* being created */ #define PF_EXITING 0x00000004 /* getting shut down */ #define PF_EXITPIDONE 0x00000008 /* pi exit done on shut down */ #define PF_VCPU 0x00000010 /* I'm a virtual CPU */ #define PF_WQ_WORKER 0x00000020 /* I'm a workqueue worker */ #define PF_FORKNOEXEC 0x00000040 /* forked but didn't exec ,进程刚创建,但还没执行*/ #define PF_MCE_PROCESS 0x00000080 /* process policy on mce errors */ #define PF_SUPERPRIV 0x00000100 /* used super-user privileges */ /*超级用户特权*/ #define PF_DUMPCORE 0x00000200 /* dumped core */ #define PF_SIGNALED 0x00000400 /* killed by a signal */ /*进程被信号杀死*/ #define PF_MEMALLOC 0x00000800 /* Allocating memory */ #define PF_USED_MATH 0x00002000 /* if unset the fpu must be initialized before use */ #define PF_FREEZING 0x00004000 /* freeze in progress. do not account to load */ #define PF_NOFREEZE 0x00008000 /* this thread should not be frozen */ #define PF_FROZEN 0x00010000 /* frozen for system suspend */ #define PF_FSTRANS 0x00020000 /* inside a filesystem transaction */ #define PF_KSWAPD 0x00040000 /* I am kswapd */ #define PF_OOM_ORIGIN 0x00080000 /* Allocating much memory to others */ #define PF_LESS_THROTTLE 0x00100000 /* Throttle me less: I clean memory */ #define PF_KTHREAD 0x00200000 /* I am a kernel thread */ #define PF_RANDOMIZE 0x00400000 /* randomize virtual address space */ #define PF_SWAPWRITE 0x00800000 /* Allowed to write to swap */ #define PF_SPREAD_PAGE 0x01000000 /* Spread page cache over cpuset */ #define PF_SPREAD_SLAB 0x02000000 /* Spread some slab caches over cpuset */ #define PF_THREAD_BOUND 0x04000000 /* Thread bound to specific cpu */ #define PF_MCE_EARLY 0x08000000 /* Early kill for mce process policy */ #define PF_MEMPOLICY 0x10000000 /* Non-default NUMA mempolicy */ #define PF_MUTEX_TESTER 0x20000000 /* Thread belongs to the rt mutex tester */ #define PF_FREEZER_SKIP 0x40000000 /* Freezer should not count it as freezable */ #define PF_FREEZER_NOSIG 0x80000000 /* Freezer won't send signals to it */
int prio, static_prio, normal_prio;unsigned int rt_priority;
字段 | 描述 |
static_prio | 用于保存静态优先级,可以通过nice系统调用来进行修改 |
rt_priority | 用于保存实时优先级 |
normal_prio | 值取决于静态优先级和调度策略 |
prio | 用于保存动态优先级 |
unsigned int policy; /*选择调度策略*/ const struct sched_class *sched_class;struct sched_entity se;struct sched_rt_entity rt; policy:表示进程的调度策略,目前主要有以下五种 #define SCHED_NORMAL 0#define SCHED_FIFO 1 /*操作系统中经常讲的,先入先出调度算法*/#define SCHED_RR 2 /*轮流调度算法*/#define SCHED_BATCH 3/* SCHED_ISO: reserved but not implemented yet */#define SCHED_IDLE 5 字段 描述 所在调度器类 SCHED_NORMAL (也叫SCHED_OTHER)用于普通进程,通过CFS调度器实现。SCHED_BATCH用于非交互的处理器消耗型进程 CFS SCHED_BATCH SCHED_NORMAL普通进程策略的分化版本。采用分时策略,根据动态优先级(可用nice()API设置),分配 CPU 运算资源。注意:这类进程比上述两类实时进程优先级低,换言之,在有实时进程存在时,实时进程优先调度。但针对吞吐量优化 CFS SCHED_IDLE 优先级最低,在系统空闲时才跑这类进程 CFS SCHED_FIFO 先入先出调度算法(实时调度策略),相同优先级的任务先到先服务,高优先级的任务可以抢占低优先级的任务 RT SCHED_RR 轮流调度算法(实时调度策略),后 者提供 Roound-Robin 语义,采用时间片,相同优先级的任务当用完时间片会被放到队列尾部,以保证公平性,同样,高优先级的任务可以抢占低优先级的任务。不同要求的实时任务可以根据需要用sched_setscheduler()API 设置策略 RT sched_class:表示调度类 se和rt都是调用实体,一个用于普通进程,一个用于实时进程,每个进程都有其中之一的实体。 (9)进程地址空间(重点来了~!!) struct mm_struct *mm, *active_mm; mm:进程所拥有的用户空间内存描述符, active_mm:进程运行时所使用的内存描述符, 注意: 对于普通进程,这两个指针变量相同 对于内核线程,不拥有任何内存描述符,mm成员总是设为NULL 当内核线程运行时,它的active_mm成员被初始化为前一个运行进程的active_mm值 内存描述符(参考我的另一篇博文:http://blog.csdn.net/tiankong_/article/details/75676131) 进程的存储空间布局(参考我的另一篇博文:http://blog.csdn.net/tiankong_/article/details/75734817) (10)信号机制相关字段 /* signal handlers */ struct signal_struct *signal; struct sighand_struct *sighand; sigset_t blocked, real_blocked; sigset_t saved_sigmask; /* restored if set_restore_sigmask() was used */ struct sigpending pending; unsigned long sas_ss_sp; size_t sas_ss_size; int (*notifier)(void *priv); void *notifier_data; sigset_t *notifier_mask; signal:指向进程的信号描述符sighand:指向进程的信号处理程序描述符 blocked:表示被阻塞信号的掩码 real_blocked:表示临时掩码 sas_ss_sp:是信号处理程序备用堆栈的地址 sas_ss_size:表示堆栈的大小 pending: struct task_struct { volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */ /*进程状态*/ void *stack; atomic_t usage; unsigned int flags; /* per process flags, defined below */ unsigned int ptrace; int lock_depth; /* BKL lock depth */#ifdef CONFIG_SMP#ifdef __ARCH_WANT_UNLOCKED_CTXSW int oncpu;#endif#endif int prio, static_prio, normal_prio; unsigned int rt_priority; const struct sched_class *sched_class; struct sched_entity se; struct sched_rt_entity rt;#ifdef CONFIG_PREEMPT_NOTIFIERS /* list of struct preempt_notifier: */ struct hlist_head preempt_notifiers;#endif /* * fpu_counter contains the number of consecutive context switches * that the FPU is used. If this is over a threshold, the lazy fpu * saving becomes unlazy to save the trap. This is an unsigned char * so that after 256 times the counter wraps and the behavior turns * lazy again; this to deal with bursty apps that only use FPU for * a short time */ unsigned char fpu_counter;#ifdef CONFIG_BLK_DEV_IO_TRACE unsigned int btrace_seq;#endif unsigned int policy; cpumask_t cpus_allowed;#ifdef CONFIG_TREE_PREEMPT_RCU int rcu_read_lock_nesting; char rcu_read_unlock_special; struct rcu_node *rcu_blocked_node; struct list_head rcu_node_entry;#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT) struct sched_info sched_info;#endif struct list_head tasks; struct plist_node pushable_tasks; struct mm_struct *mm, *active_mm;#if defined(SPLIT_RSS_COUNTING) struct task_rss_stat rss_stat;#endif/* task state */ int exit_state; int exit_code, exit_signal; int pdeath_signal; /* The signal sent when the parent dies */ /* ??? */ unsigned int personality; unsigned did_exec:1; unsigned in_execve:1; /* Tell the LSMs that the process is doing an * execve */ unsigned in_iowait:1; /* Revert to default priority/policy when forking */ unsigned sched_reset_on_fork:1; pid_t pid; pid_t tgid;#ifdef CONFIG_CC_STACKPROTECTOR /* Canary value for the -fstack-protector gcc feature */ unsigned long stack_canary;#endif /* * pointers to (original) parent process, youngest child, younger sibling, * older sibling, respectively. (p->father can be replaced with * p->real_parent->pid) */ struct task_struct *real_parent; /* real parent process */ struct task_struct *parent; /* recipient of SIGCHLD, wait4() reports */ /* * children/sibling forms the list of my natural children */ struct list_head children; /* list of my children */ struct list_head sibling; /* linkage in my parent's children list */ struct task_struct *group_leader; /* threadgroup leader */ /* * ptraced is the list of tasks this task is using ptrace on. * This includes both natural children and PTRACE_ATTACH targets. * p->ptrace_entry is p's link on the p->parent->ptraced list. */ struct list_head ptraced; struct list_head ptrace_entry; /* * This is the tracer handle for the ptrace BTS extension. * This field actually belongs to the ptracer task. */ struct bts_context *bts; /* PID/PID hash table linkage. */ struct pid_link pids[PIDTYPE_MAX]; struct list_head thread_group; struct completion *vfork_done; /* for vfork() */ int __user *set_child_tid; /* CLONE_CHILD_SETTID */ int __user *clear_child_tid; /* CLONE_CHILD_CLEARTID */ cputime_t utime, stime, utimescaled, stimescaled; cputime_t gtime;#ifndef CONFIG_VIRT_CPU_ACCOUNTING cputime_t prev_utime, prev_stime;#endif unsigned long nvcsw, nivcsw; /* context switch counts */ struct timespec start_time; /* monotonic time */ struct timespec real_start_time; /* boot based time *//* mm fault and swap info: this can arguably be seen as either mm-specific or thread-specific */ unsigned long min_flt, maj_flt; struct task_cputime cputime_expires; struct list_head cpu_timers[3];/* process credentials */ const struct cred *real_cred; /* objective and real subjective task * credentials (COW) */ const struct cred *cred; /* effective (overridable) subjective task * credentials (COW) */ struct mutex cred_guard_mutex; /* guard against foreign influences on * credential calculations * (notably. ptrace) */ struct cred *replacement_session_keyring; /* for KEYCTL_SESSION_TO_PARENT */ char comm[TASK_COMM_LEN]; /* executable name excluding path - access with [gs]et_task_comm (which lock it with task_lock()) - initialized normally by setup_new_exec *//* file system info */ int link_count, total_link_count;#ifdef CONFIG_SYSVIPC/* ipc stuff */ struct sysv_sem sysvsem;#endif#ifdef CONFIG_DETECT_HUNG_TASK/* hung task detection */ unsigned long last_switch_count;#endif/* CPU-specific state of this task */ struct thread_struct thread;/* filesystem information */ struct fs_struct *fs;/* open file information */ struct files_struct *files;/* namespaces */ struct nsproxy *nsproxy;/* signal handlers */ struct signal_struct *signal; struct sighand_struct *sighand; sigset_t blocked, real_blocked; sigset_t saved_sigmask; /* restored if set_restore_sigmask() was used */ struct sigpending pending; unsigned long sas_ss_sp; size_t sas_ss_size; int (*notifier)(void *priv); void *notifier_data; sigset_t *notifier_mask; struct audit_context *audit_context;#ifdef CONFIG_AUDITSYSCALL uid_t loginuid; unsigned int sessionid;#endif seccomp_t seccomp;/* Thread group tracking */ u32 parent_exec_id; u32 self_exec_id;/* Protection of (de-)allocation: mm, files, fs, tty, keyrings, mems_allowed, * mempolicy */ spinlock_t alloc_lock;#ifdef CONFIG_GENERIC_HARDIRQS /* IRQ handler threads */ struct irqaction *irqaction;#endif /* Protection of the PI data structures: */ raw_spinlock_t pi_lock;#ifdef CONFIG_RT_MUTEXES /* PI waiters blocked on a rt_mutex held by this task */ struct plist_head pi_waiters; /* Deadlock detection and priority inheritance handling */ struct rt_mutex_waiter *pi_blocked_on;#endif#ifdef CONFIG_DEBUG_MUTEXES /* mutex deadlock detection */ struct mutex_waiter *blocked_on;#endif#ifdef CONFIG_TRACE_IRQFLAGS unsigned int irq_events; unsigned long hardirq_enable_ip; unsigned long hardirq_disable_ip; unsigned int hardirq_enable_event; unsigned int hardirq_disable_event; int hardirqs_enabled; int hardirq_context; unsigned long softirq_disable_ip; unsigned long softirq_enable_ip; unsigned int softirq_disable_event; unsigned int softirq_enable_event; int softirqs_enabled; int softirq_context;#endif#ifdef CONFIG_LOCKDEP# define MAX_LOCK_DEPTH 48UL u64 curr_chain_key; int lockdep_depth; unsigned int lockdep_recursion; struct held_lock held_locks[MAX_LOCK_DEPTH]; gfp_t lockdep_reclaim_gfp;#endif/* journalling filesystem info */ void *journal_info;/* stacked block device info */ struct bio_list *bio_list;/* VM state */ struct reclaim_state *reclaim_state; struct backing_dev_info *backing_dev_info; struct io_context *io_context; unsigned long ptrace_message; siginfo_t *last_siginfo; /* For ptrace use. */ struct task_io_accounting ioac;#if defined(CONFIG_TASK_XACCT) u64 acct_rss_mem1; /* accumulated rss usage */ u64 acct_vm_mem1; /* accumulated virtual memory usage */ cputime_t acct_timexpd; /* stime + utime since last update */#endif#ifdef CONFIG_CPUSETS nodemask_t mems_allowed; /* Protected by alloc_lock */ int cpuset_mem_spread_rotor;#endif#ifdef CONFIG_CGROUPS /* Control Group info protected by css_set_lock */ struct css_set *cgroups; /* cg_list protected by css_set_lock and tsk->alloc_lock */ struct list_head cg_list;#endif#ifdef CONFIG_FUTEX struct robust_list_head __user *robust_list;#ifdef CONFIG_COMPAT struct compat_robust_list_head __user *compat_robust_list;#endif struct list_head pi_state_list; struct futex_pi_state *pi_state_cache;#endif#ifdef CONFIG_PERF_EVENTS struct perf_event_context *perf_event_ctxp; struct mutex perf_event_mutex; struct list_head perf_event_list;#endif#ifdef CONFIG_NUMA struct mempolicy *mempolicy; /* Protected by alloc_lock */ short il_next;#endif atomic_t fs_excl; /* holding fs exclusive resources */ struct rcu_head rcu; /* * cache last used pipe for splice */ struct pipe_inode_info *splice_pipe;#ifdef CONFIG_TASK_DELAY_ACCT struct task_delay_info *delays;#endif#ifdef CONFIG_FAULT_INJECTION int make_it_fail;#endif struct prop_local_single dirties;#ifdef CONFIG_LATENCYTOP int latency_record_count; struct latency_record latency_record[LT_SAVECOUNT];#endif /* * time slack values; these are used to round up poll() and * select() etc timeout values. These are in nanoseconds. */ unsigned long timer_slack_ns; unsigned long default_timer_slack_ns; struct list_head *scm_work_list;#ifdef CONFIG_FUNCTION_GRAPH_TRACER /* Index of current stored address in ret_stack */ int curr_ret_stack; /* Stack of return addresses for return function tracing */ struct ftrace_ret_stack *ret_stack; /* time stamp for last schedule */ unsigned long long ftrace_timestamp; /* * Number of functions that haven't been traced * because of depth overrun. */ atomic_t trace_overrun; /* Pause for the tracing */ atomic_t tracing_graph_pause;#endif#ifdef CONFIG_TRACING /* state flags for use by tracers */ unsigned long trace; /* bitmask of trace recursion */ unsigned long trace_recursion;#endif /* CONFIG_TRACING */#ifdef CONFIG_CGROUP_MEM_RES_CTLR /* memcg uses this to do batch job */ struct memcg_batch_info { int do_batch; /* incremented when batch uncharge started */ struct mem_cgroup *memcg; /* target memcg of uncharge */ unsigned long bytes; /* uncharged usage */ unsigned long memsw_bytes; /* uncharged mem+swap usage */ } memcg_batch;#endif};