signal

signal

信号提供一种机制，告诉用户进程发生了那些异常。

linux信号量

sigaction 函数

int sigaction(int signum, // 信号量
			  const struct sigaction *act, // 设置对信号量新的处理方式
			  struct sigaction *oldact);   // oldact如果非空，会将原来的信号量处理方式保存到oldact
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sigaction结构体

struct sigaction {
    void     (*sa_handler)(int);
    void     (*sa_sigaction)(int, siginfo_t*, void*);
    sigset_t   sa_mask;
    int        sa_flags;
    void     (*sa_restorer)(void);
};
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• sa_handle, 指定信号捕捉后的处理函数名(即注册函数)。也可赋值为

  • SIG_IGN表忽略
  • SIG_DFL表执行默认动作

• sa_sigaction, 如果sa_flags 设置了SA_SIGINFO， sa_sigaction可以替代sa_handle指定信号捕捉后处理函数名(即注册函数)

  • int, signal num
  • siginfo_t *
  • ucontext_t (cast to void *)

• sa_flags, 修改信号行为的标志

• sa_mask, 调用信号处理函数时，所要屏蔽的信号集合

• sa_restorer, 为了返回旧的信号处理程序，但现在应该是已经弃用了

• SA_ONSTACK 在信号处理程序的执行期间使用备用信号堆栈。[1,2]

  Here is one example…a process has a limit on the size of the stack. If a process exceeds that limit it will get a signal, often SIGSEGV, but it can vary from os to os. Now, how can you catch that signal? Without an alternate stack, the signal handler could never run.

  I had this exact situation once. A process was dying from a blown stack but its current directory was in a filesystem that was too small to hold a core dump. My handler needed to catch the signal, cd to a large filesystem, set the signal action back to default, and resend the signal to itself. I could not have done that without an alternate stack.

  That was the only time that I needed an alternate stack.

• SA_RESTART, 当信号处理函数返回后, 被该信号中断的系统调用将自动恢复.[3]

• SA_SIGINFO， sa_sigaction可以替代sa_handle指定信号捕捉后处理函数名(即注册函数)

siginfo_t

typedef struct {
    int si_signo;
    int si_code;
    union sigval si_value;
    int si_errno;
    pid_t si_pid;
    uid_t si_uid;
    void *si_addr;
    int si_status;
    int si_band;
} siginfo_t;
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• si_signo, signal number
• si_code
• si_errno
• si_pid, 发送该信息的进程pid
• si_uid, 发送该信息的用户uid
• si_addr, 错误发生的地址

sigaddset

int sigaddset(sigset_t *set, int signum);
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typedef struct {
	unsigned long sig[_NSIG_WORDS]；
} sigset_t
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sigemptyset

int sigemptyset(sigset_t *set)
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将参数set信号集初始化并清空

pthread_sigmask

屏蔽某个线程对某些信号的 响应处理

int pthread_sigmask(int how, const sigset_t *set, sigset_t *oldset);
How:
SIG_BLOCK:     结果集是当前集合参数集的并集
SIG_UNBLOCK: 结果集是当前集合参数集的差集
SIG_SETMASK: 结果集是由参数集指向的集
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sigfillset

int sigfillset(sigset_t *set);
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set指向的信号集中将包含linux支持的信号量

sigdelset

int sigdelset(sigset_t *set, int signum);
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在set指向的信号集中删除signum信号

ucontext_t

// ucontext.h
typedef struct ucontext {
  unsigned long int uc_flags;
  struct ucontext *uc_link; // 指向一个上下文，当当前上下文结束时，将返回执行该上下文
  stack_t uc_stack; // 栈信息
  mcontext_t uc_mcontext; // 保存上下文的各种寄存器信息
  __sigset_t uc_sigmask; // 屏蔽的信号量集合
  struct _libc_fpstate __fpregs_mem;
} ucontext_t;
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stack_t

typedef struct {
  void *ss_sp; // 栈空间指针,指向当前栈所在的位置
  int ss_flags; // 栈空间的flags
  size_t ss_size; // 整个栈的大小
} stack_t;
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mcontext_t