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OS (:recycle:structure (:three:Monolithic Kernels (:sweat_drops…

- - - - :one:difficult to modify
      - :two:difficult to isolate bugs and errors
      - :three:kernel gets bigger as the OS develops
  - - - :one:easier to extend
      - :two:easier to port the microkernel system to other architectures
      - :three:more reliable
        
        :bread:less code in running kernel
      - :four:more secure
- - - - :icecream:examples
        
        :one:set the value of clock
        
        :two:clear memory
        
        :three:switch from user mode to kernel mode
        
        :four:I/O
        
        :five:turn off interrupts
        
        :six:modify entries in device-status table
    - - :icecream:examples
        
        :one:issue a trap instruction
        
        :two:read the clock
        
        :three:switch from user mode to kernel mode
      - :apple:switch to kernel mode
        
        :one:interrupt
        
        :two:trap
        
        :three:system call
    - - :bread:every second, the timer interrupts the program, decrements the counter and check if the count equals to 0
      - :checkered_flag:avoid that a program never return control or get stuck in an infinite loop
      - :icecream:A program with 7-minute time limit would have its timer initialized to 420
  - - - :pencil2:strace <cmd> can list all the system calls executed by this command
    - - :pencil2:include/asm-i386/unistd.h 或 include/uapi/asm-generic/unistd.h
      - #define __NR_restart_syscall 0 #define __NR_exit 1 #define __NR_fork 2 #define __NR_read 3 ...
    - - :bread:详见评论
      - :explode: libc => 中断 => system_call(找服务例程 => 执行服务例程) => 返回
      - :globe_with_meridians:服务例程
        
        :mega:内核函数
        
        :explode:由系统调用调用
- - - - :explode: a monitor is a synchronization construct that allows threads to have both mutual exclusion and the ability to wait (block) for a certain condition to become true.