【linux进程通信】信号的使用

关于信号：

信号的作用：
1，通知进程一些特定的事件
2，强迫进程执行他自己代码中间的对信号的处理程序

进程以三种方式对一个信号作出应答：
1，显示忽略
2，执行信号相关的缺省操作

• terminate 终止
• Dump 终止并且保存信息用于调试
• Ignore 忽略
• Stop 停止，进程状态为 TASK_STOPPED
• Continue 如果进程停止，就将状态置为 TASK_RUNNING

3，调用相应的信号处理函数捕获信号（信号处理函数必须是柯重入的）

信号的分类

常规信号 前1~31号 同种类型的常规信号不需要排队接收
实时信号 POSIX标准引入 32~64位信号，需要排队以便多个信号被接受

关于信号的操作流程
*以下均有API可供查阅

• 产生信号
• 传递信号
• 执行信号的缺省操作
• 捕获信号

小例子
关于signal的用法：
函数作用，类似sigaction，改变与信号相关的操作
@signum 捕获的信号量
@sighandler_t 信号的处理函数

• SIG_IGN:忽略信号
• SIG_DFL:恢复信号的默认行为

#include 
#include 

/*

    ctrl-c 发送 SIGINT 信号给前台进程组中的所有进程。常用于终止正在运行的程序。
    ctrl-z 发送 SIGTSTP 信号给前台进程组中的所有进程，常用于挂起一个进程。
    ctrl-d 不是发送信号，而是表示一个特殊的二进制值，表示 EOF。
    ctrl-\ 发送 SIGQUIT 信号给前台进程组中的所有进程，终止前台进程并生成 core 文件。

  */
void ouch(int sig)
{
    printf("\nOUCH! - I got signal %d\n", sig);
    //恢复终端中断信号SIGINT的默认行为
    //(void) signal(SIGINT, SIG_DFL);
}
void refuse(int sig){
    printf("no i do not quit ! \n");
    signal(SIGTSTP, SIG_DFL);
}

int main()
{
    //改变终端中断信号SIGINT的默认行为，使之执行ouch函数
    //而不是终止程序的执行
   (void) signal(SIGINT, ouch);
    //(void) signal(SIGQUIT,refuse); ctl——z 无法捕获到，不知道为什么
    while(1)
    {
        printf("Hello World!\n");
        sleep(1);
    }
    return 0;
}

相关结构体

struct task_struct {
    volatile long state;    /* -1 unrunnable, 0 runnable, >0 stopped */
    void *stack;
    atomic_t usage;
    unsigned int flags; /* per process flags, defined below */
    unsigned int ptrace;

#ifdef CONFIG_SMP
    struct llist_node wake_entry;
    int on_cpu;
#endif
    int on_rq;

    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_SCHED_HMP
    struct ravg ravg;
#endif
#ifdef CONFIG_CGROUP_SCHED
    struct task_group *sched_task_group;
#endif

#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;
    int nr_cpus_allowed;
    cpumask_t cpus_allowed;

#ifdef CONFIG_PREEMPT_RCU
    int rcu_read_lock_nesting;
    char rcu_read_unlock_special;
    struct list_head rcu_node_entry;
#endif /* #ifdef CONFIG_PREEMPT_RCU */
#ifdef CONFIG_TREE_PREEMPT_RCU
    struct rcu_node *rcu_blocked_node;
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
#ifdef CONFIG_RCU_BOOST
    struct rt_mutex *rcu_boost_mutex;
#endif /* #ifdef CONFIG_RCU_BOOST */

#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
    struct sched_info sched_info;
#endif

    struct list_head tasks;
#ifdef CONFIG_SMP
    struct plist_node pushable_tasks;
#endif

    struct mm_struct *mm, *active_mm;
#ifdef CONFIG_COMPAT_BRK
    unsigned brk_randomized:1;
#endif
#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 jobctl;    /* JOBCTL_*, siglock protected */

    /* Used for emulating ABI behavior of previous Linux versions */
    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;
    unsigned sched_contributes_to_load:1;

    unsigned long atomic_flags; /* Flags needing atomic access. */

    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 __rcu *real_parent; /* real parent process */
    struct task_struct __rcu *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;

    /* PID/PID hash table linkage. */
    struct pid_link pids[PIDTYPE_MAX];
    struct list_head thread_group;
    struct list_head thread_node;

    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;
    unsigned long long cpu_power;
#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
    struct cputime prev_cputime;
#endif
#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
    seqlock_t vtime_seqlock;
    unsigned long long vtime_snap;
    enum {
        VTIME_SLEEPING = 0,
        VTIME_USER,
        VTIME_SYS,
    } vtime_snap_whence;
#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 __rcu *real_cred; /* objective and real subjective task
                     * credentials (COW) */
    const struct cred __rcu *cred;  /* effective (overridable) subjective task
                     * credentials (COW) */
    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;//进程信号描述符
    struct sighand_struct *sighand; //信号处理程序描述符

    sigset_t blocked, real_blocked;//被阻塞信号的掩码，临时掩码
    sigset_t saved_sigmask; /* restored if set_restore_sigmask() was used */
    struct sigpending pending; //存放私有挂起信号

    unsigned long sas_ss_sp; //信号处理程序备用堆栈地址
    size_t sas_ss_size; //堆栈大小
    int (*notifier)(void *priv); //函数指针，设备驱动用这个函数阻塞进程的某些信号
    void *notifier_data;//notifier 函数的参数
    sigset_t *notifier_mask;//函数所阻塞信号的位掩码
    struct callback_head *task_works;

    struct audit_context *audit_context;
#ifdef CONFIG_AUDITSYSCALL
    kuid_t loginuid;
    unsigned int sessionid;
#endif
    struct seccomp 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;

    /* 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;

#ifdef CONFIG_BLOCK
/* stack plugging */
    struct blk_plug *plug;
#endif

/* 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 */
    seqcount_t mems_allowed_seq;    /* Seqence no to catch updates */
    int cpuset_mem_spread_rotor;
    int cpuset_slab_spread_rotor;
#endif
#ifdef CONFIG_CGROUPS
    /* Control Group info protected by css_set_lock */
    struct css_set __rcu *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[perf_nr_task_contexts];
    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;
    short pref_node_fork;
#endif
#ifdef CONFIG_NUMA_BALANCING
    int numa_scan_seq;
    int numa_migrate_seq;
    unsigned int numa_scan_period;
    u64 node_stamp;         /* migration stamp  */
    struct callback_head numa_work;
#endif /* CONFIG_NUMA_BALANCING */

    struct rcu_head rcu;

    /*
     * cache last used pipe for splice
     */
    struct pipe_inode_info *splice_pipe;

    struct page_frag task_frag;

#ifdef  CONFIG_TASK_DELAY_ACCT
    struct task_delay_info *delays;
#endif
#ifdef CONFIG_FAULT_INJECTION
    int make_it_fail;
#endif
    /*
     * when (nr_dirtied >= nr_dirtied_pause), it's time to call
     * balance_dirty_pages() for some dirty throttling pause
     */
    int nr_dirtied;
    int nr_dirtied_pause;
    unsigned long dirty_paused_when; /* start of a write-and-pause period */

#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;

#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 and counter of trace recursion */
    unsigned long trace_recursion;
#endif /* CONFIG_TRACING */
#ifdef CONFIG_MEMCG /* 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 nr_pages; /* uncharged usage */
        unsigned long memsw_nr_pages; /* uncharged mem+swap usage */
    } memcg_batch;
    unsigned int memcg_kmem_skip_account;
#endif
#ifdef CONFIG_HAVE_HW_BREAKPOINT
    atomic_t ptrace_bp_refcnt;
#endif
#ifdef CONFIG_UPROBES
    struct uprobe_task *utask;
#endif
#if defined(CONFIG_BCACHE) || defined(CONFIG_BCACHE_MODULE)
    unsigned int    sequential_io;
    unsigned int    sequential_io_avg;
#endif
};

信号描述符 signal_struct

/*
 * NOTE! "signal_struct" does not have its own
 * locking, because a shared signal_struct always
 * implies a shared sighand_struct, so locking
 * sighand_struct is always a proper superset of
 * the locking of signal_struct.
 */
struct signal_struct {
    atomic_t        sigcnt;//使用计数器
    atomic_t        live;//线程组中活动的进程数量
    int         nr_threads;
    struct list_head    thread_head;

    wait_queue_head_t   wait_chldexit;  /* for wait4() *///在系统调用wait4中睡眠的进程等待队列

    /* current thread group signal load-balancing target: */
    struct task_struct  *curr_target;//接收信号的县城住中间最后一个进程的描述符

    /* shared signal handling: */
    struct sigpending   shared_pending;//共享挂起信号

    /* thread group exit support */
    int         group_exit_code; //线程组的进程终止码
    /* overloaded:
     * - notify group_exit_task when ->count is equal to notify_count
     * - everyone except group_exit_task is stopped during signal delivery
     *   of fatal signals, group_exit_task processes the signal.
     */
    int         notify_count;  //在杀死整个线程组的时候使用
    struct task_struct  *group_exit_task;//在杀死整个线程组的时候使用

    /* thread group stop support, overloads group_exit_code too */
    int         group_stop_count; //在  停止 整个线程组的时候使用
    unsigned int        flags; /* see SIGNAL_* flags below */

    /*
     * PR_SET_CHILD_SUBREAPER marks a process, like a service
     * manager, to re-parent orphan (double-forking) child processes
     * to this process instead of 'init'. The service manager is
     * able to receive SIGCHLD signals and is able to investigate
     * the process until it calls wait(). All children of this
     * process will inherit a flag if they should look for a
     * child_subreaper process at exit.
     */
    unsigned int        is_child_subreaper:1;
    unsigned int        has_child_subreaper:1;

    /* POSIX.1b Interval Timers */
    int         posix_timer_id;
    struct list_head    posix_timers;

    /* ITIMER_REAL timer for the process */
    struct hrtimer real_timer;
    struct pid *leader_pid;
    ktime_t it_real_incr;

    /*
     * ITIMER_PROF and ITIMER_VIRTUAL timers for the process, we use
     * CPUCLOCK_PROF and CPUCLOCK_VIRT for indexing array as these
     * values are defined to 0 and 1 respectively
     */
    struct cpu_itimer it[2];

    /*
     * Thread group totals for process CPU timers.
     * See thread_group_cputimer(), et al, for details.
     */
    struct thread_group_cputimer cputimer;

    /* Earliest-expiration cache. */
    struct task_cputime cputime_expires;

    struct list_head cpu_timers[3];

    struct pid *tty_old_pgrp;

    /* boolean value for session group leader */
    int leader;

    struct tty_struct *tty; /* NULL if no tty */

#ifdef CONFIG_SCHED_AUTOGROUP
    struct autogroup *autogroup;
#endif
    /*
     * Cumulative resource counters for dead threads in the group,
     * and for reaped dead child processes forked by this group.
     * Live threads maintain their own counters and add to these
     * in __exit_signal, except for the group leader.
     */
    cputime_t utime, stime, cutime, cstime;
    cputime_t gtime;
    cputime_t cgtime;
#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
    struct cputime prev_cputime;
#endif
    unsigned long nvcsw, nivcsw, cnvcsw, cnivcsw;
    unsigned long min_flt, maj_flt, cmin_flt, cmaj_flt;
    unsigned long inblock, oublock, cinblock, coublock;
    unsigned long maxrss, cmaxrss;
    struct task_io_accounting ioac;

    /*
     * Cumulative ns of schedule CPU time fo dead threads in the
     * group, not including a zombie group leader, (This only differs
     * from jiffies_to_ns(utime + stime) if sched_clock uses something
     * other than jiffies.)
     */
    unsigned long long sum_sched_runtime;

    /*
     * We don't bother to synchronize most readers of this at all,
     * because there is no reader checking a limit that actually needs
     * to get both rlim_cur and rlim_max atomically, and either one
     * alone is a single word that can safely be read normally.
     * getrlimit/setrlimit use task_lock(current->group_leader) to
     * protect this instead of the siglock, because they really
     * have no need to disable irqs.
     */
    struct rlimit rlim[RLIM_NLIMITS];

#ifdef CONFIG_BSD_PROCESS_ACCT
    struct pacct_struct pacct;  /* per-process accounting information */
#endif
#ifdef CONFIG_TASKSTATS
    struct taskstats *stats;
#endif
#ifdef CONFIG_AUDIT
    unsigned audit_tty;
    unsigned audit_tty_log_passwd;
    struct tty_audit_buf *tty_audit_buf;
#endif
#ifdef CONFIG_CGROUPS
    /*
     * group_rwsem prevents new tasks from entering the threadgroup and
     * member tasks from exiting,a more specifically, setting of
     * PF_EXITING.  fork and exit paths are protected with this rwsem
     * using threadgroup_change_begin/end().  Users which require
     * threadgroup to remain stable should use threadgroup_[un]lock()
     * which also takes care of exec path.  Currently, cgroup is the
     * only user.
     */
    struct rw_semaphore group_rwsem;
#endif

    oom_flags_t oom_flags;
    short oom_score_adj;        /* OOM kill score adjustment */
    short oom_score_adj_min;    /* OOM kill score adjustment min value.
                     * Only settable by CAP_SYS_RESOURCE. */

    struct mutex cred_guard_mutex;  /* guard against foreign influences on
                     * credential calculations
                     * (notably. ptrace) */
};

信号处理程序描述符：

struct sighand_struct {
    atomic_t        count; //计数器
    struct k_sigaction  action[_NSIG];//在所传递的信号上执行操作的结构数组
    spinlock_t      siglock;//保护信号描述符和信号处理函数的描述符的自旋锁
    wait_queue_head_t   signalfd_wqh;
};