知识一点一点的积累,如果有前辈看有错误的地方请指出,我好尽快改正
进程的四要素：
1，首先要有一段程序供进程运行，也就是说，就像一个剧本一样，而剧本可以有很多剧团一起用，一起来参考剧本演戏。
2。进程都有起码的“私有财产”，就是说每个进程都会有进程专用的系统堆栈空间。
3。每个进程都会有一个相应的数据结构，也就是PCB（进程控制块），其数据结构如下：
Linux/include/linux/sched.h 中
801 struct task_struct {
802 volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped 描述进程状态的*/
803 struct thread_info *thread_info;
804 atomic_t usage;
805 unsigned long flags; /* 描述进程标志的per process flags, defined below */
806 unsigned long ptrace;
807
808 int lock_depth; /* BKL lock depth */
809
810 #ifdef CONFIG_SMP
811 #ifdef __ARCH_WANT_UNLOCKED_CTXSW
812 int oncpu;
813 #endif
814 #endif
815 int load_weight; /* for niceness load balancing purposes */
816 int prio, static_prio, normal_prio;
817 struct list_head run_list;
818 struct prio_array *array;
819
820 unsigned short ioprio;
821 #ifdef CONFIG_BLK_DEV_IO_TRACE
822 unsigned int btrace_seq;
823 #endif
824 unsigned long sleep_avg;
825 unsigned long long timestamp, last_ran;
826 unsigned long long sched_time; /* sched_clock time spent running */
827 enum sleep_type sleep_type;
828
829 unsigned long policy;
830 cpumask_t cpus_allowed;
831 unsigned int time_slice, first_time_slice;
832
833 #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
834 struct sched_info sched_info;
835 #endif
836
837 struct list_head tasks;
838 /*
839 * ptrace_list/ptrace_children forms the list of my children
840 * that were stolen by a ptracer.
841 */
842 struct list_head ptrace_children;
843 struct list_head ptrace_list;
844
845 struct mm_struct *mm, *active_mm;
846
847 /* task state */
848 struct linux_binfmt *binfmt;
849 long exit_state;
850 int exit_code, exit_signal;
851 int pdeath_signal; /* The signal sent when the parent dies */
852 /* ??? */
853 unsigned long personality;
854 unsigned did_exec:1;
855 pid_t pid;/*进程id*/
856 pid_t tgid;
857
858 #ifdef CONFIG_CC_STACKPROTECTOR
859 /* Canary value for the -fstack-protector gcc feature */
860 unsigned long stack_canary;
861 #endif
862 /*
863 * pointers to (original) parent process, youngest child, younger sibling,
864 * older sibling, respectively. (p->father can be replaced with
865 * p->parent->pid)
866 */
867 struct task_struct *real_parent; /* real parent process (when being debugged) */
868 struct task_struct *parent; /*父进程 parent process */
869 /*
870 * children/sibling forms the list of my children plus the
871 * tasks I'm ptracing.
872 */
873 struct list_head children; /* 子进程list of my children */
874 struct list_head sibling; /* linkage in my parent's children list */
875 struct task_struct *group_leader; /* threadgroup leader */
876
877 /* PID/PID hash table linkage. */
878 struct pid_link pids[PIDTYPE_MAX];
879 struct list_head thread_group;
880
881 struct completion *vfork_done; /* for vfork() */
882 int __user *set_child_tid; /* CLONE_CHILD_SETTID */
883 int __user *clear_child_tid; /* CLONE_CHILD_CLEARTID */
884
885 unsigned long rt_priority;
886 cputime_t utime, stime;
887 unsigned long nvcsw, nivcsw; /* context switch counts */
888 struct timespec start_time;
889 /* mm fault and swap info: this can arguably be seen as either mm-specific or thread-specific */
890 unsigned long min_flt, maj_flt;
891
892 cputime_t it_prof_expires, it_virt_expires;
893 unsigned long long it_sched_expires;
894 struct list_head cpu_timers[3];
895
896 /* process credentials */
897 uid_t uid,euid,suid,fsuid;
898 gid_t gid,egid,sgid,fsgid;
899 struct group_info *group_info;
900 kernel_cap_t cap_effective, cap_inheritable, cap_permitted;
901 unsigned keep_capabilities:1;
902 struct user_struct *user;
903 #ifdef CONFIG_KEYS
904 struct key *request_key_auth; /* assumed request_key authority */
905 struct key *thread_keyring; /* keyring private to this thread */
906 unsigned char jit_keyring; /* default keyring to attach requested keys to */
907 #endif
908 /*
909 * fpu_counter contains the number of consecutive context switches
910 * that the FPU is used. If this is over a threshold, the lazy fpu
911 * saving becomes unlazy to save the trap. This is an unsigned char
912 * so that after 256 times the counter wraps and the behavior turns
913 * lazy again; this to deal with bursty apps that only use FPU for
914 * a short time
915 */
916 unsigned char fpu_counter;
917 int oomkilladj; /* OOM kill score adjustment (bit shift). */
918 char comm[TASK_COMM_LEN]; /* executable name excluding path
919 - access with [gs]et_task_comm (which lock
920 it with task_lock())
921 - initialized normally by flush_old_exec */
922 /* file system info */
923 int link_count, total_link_count;
924 #ifdef CONFIG_SYSVIPC
925 /* ipc stuff */
926 struct sysv_sem sysvsem;
927 #endif
928 /* CPU-specific state of this task */
929 struct thread_struct thread;
930 /* filesystem information */
931 struct fs_struct *fs;
932 /* open file information */
933 struct files_struct *files;
934 /* namespaces */
935 struct nsproxy *nsproxy;
936 /* signal handlers */
937 struct signal_struct *signal;
938 struct sighand_struct *sighand;
939
940 sigset_t blocked, real_blocked;
941 sigset_t saved_sigmask; /* To be restored with TIF_RESTORE_SIGMASK */
942 struct sigpending pending;
943
944 unsigned long sas_ss_sp;
945 size_t sas_ss_size;
946 int (*notifier)(void *priv);
947 void *notifier_data;
948 sigset_t *notifier_mask;
949
950 void *security;
951 struct audit_context *audit_context;
952 seccomp_t seccomp;
953
954 /* Thread group tracking */
955 u32 parent_exec_id;
956 u32 self_exec_id;
957 /* Protection of (de-)allocation: mm, files, fs, tty, keyrings */
958 spinlock_t alloc_lock;
959
960 /* Protection of the PI data structures: */
961 spinlock_t pi_lock;
962
963 #ifdef CONFIG_RT_MUTEXES
964 /* PI waiters blocked on a rt_mutex held by this task */
965 struct plist_head pi_waiters;
966 /* Deadlock detection and priority inheritance handling */
967 struct rt_mutex_waiter *pi_blocked_on;
968 #endif
969
970 #ifdef CONFIG_DEBUG_MUTEXES
971 /* mutex deadlock detection */
972 struct mutex_waiter *blocked_on;
973 #endif
974 #ifdef CONFIG_TRACE_IRQFLAGS
975 unsigned int irq_events;
976 int hardirqs_enabled;
977 unsigned long hardirq_enable_ip;
978 unsigned int hardirq_enable_event;
979 unsigned long hardirq_disable_ip;
980 unsigned int hardirq_disable_event;
981 int softirqs_enabled;
982 unsigned long softirq_disable_ip;
983 unsigned int softirq_disable_event;
984 unsigned long softirq_enable_ip;
985 unsigned int softirq_enable_event;
986 int hardirq_context;
987 int softirq_context;
988 #endif
989 #ifdef CONFIG_LOCKDEP
990 # define MAX_LOCK_DEPTH 30UL
991 u64 curr_chain_key;
992 int lockdep_depth;
993 struct held_lock held_locks[MAX_LOCK_DEPTH];
994 unsigned int lockdep_recursion;
995 #endif
996
997 /* journalling filesystem info */
998 void *journal_info;
999
1000 /* VM state */
1001 struct reclaim_state *reclaim_state;
1002
1003 struct backing_dev_info *backing_dev_info;
1004
1005 struct io_context *io_context;
1006
1007 unsigned long ptrace_message;
1008 siginfo_t *last_siginfo; /* For ptrace use. */
1009 /*
1010 * current io wait handle: wait queue entry to use for io waits
1011 * If this thread is processing aio, this points at the waitqueue
1012 * inside the currently handled kiocb. It may be NULL (i.e. default
1013 * to a stack based synchronous wait) if its doing sync IO.
1014 */
1015 wait_queue_t *io_wait;
1016 /* i/o counters(bytes read/written, #syscalls */
1017 u64 rchar, wchar, syscr, syscw;
1018 struct task_io_accounting ioac;
1019 #if defined(CONFIG_TASK_XACCT)
1020 u64 acct_rss_mem1; /* accumulated rss usage */
1021 u64 acct_vm_mem1; /* accumulated virtual memory usage */
1022 cputime_t acct_stimexpd;/* stime since last update */
1023 #endif
1024 #ifdef CONFIG_NUMA
1025 struct mempolicy *mempolicy;
1026 short il_next;
1027 #endif
1028 #ifdef CONFIG_CPUSETS
1029 struct cpuset *cpuset;
1030 nodemask_t mems_allowed;
1031 int cpuset_mems_generation;
1032 int cpuset_mem_spread_rotor;
1033 #endif
1034 struct robust_list_head __user *robust_list;
1035 #ifdef CONFIG_COMPAT
1036 struct compat_robust_list_head __user *compat_robust_list;
1037 #endif
1038 struct list_head pi_state_list;
1039 struct futex_pi_state *pi_state_cache;
1040
1041 atomic_t fs_excl; /* holding fs exclusive resources */
1042 struct rcu_head rcu;
1043
1044 /*
1045 * cache last used pipe for splice
1046 */
1047 struct pipe_inode_info *splice_pipe;
1048 #ifdef CONFIG_TASK_DELAY_ACCT
1049 struct task_delay_info *delays;
1050 #endif
1051 #ifdef CONFIG_FAULT_INJECTION
1052 int make_it_fail;
1053 #endif
1054 };
|
上面的数据结构（也就是进程控制快）里包含了进程的各种信息。
4。有独立的存储空间，也就是进程的专有空间，除了前面说的系统空间堆栈空间还有用户空间堆栈。系统空间是不能独立的，任何进程都不能直接改变系统空间的内容（除了使用系统调用），除非是进程本身的系统空间堆栈以外。
如果缺少以上四个要素中的任何一个，那就不能叫进程了，如果缺了其中的第四个条件且具备其他三个要素的话，就应该称之为线程，线程分为内核线程和用户线程，内核线程指的是完全没有用户空间的，用户线程是指共享用户空间了。
阅读(1855) | 评论(2) | 转发(0) |
