The response process of the signal

Come on! Review what is the unreliable signal? Think for a while???

Signal execution site is the kernel to help us decorate, so if a signal is performing a behavior, at this time embarrassed to have a signal, then, the first behavior will be the second behavior is overwritten.

Solve the unreliable----> reentrant function: The first call is not finished, the second call comes, but does not error;

All system calls are reentrant, and some library functions can be re-entered.

Eg:open Read memcpy rand a lot more ...

int rand (void): Non-reentrant: Generates a pseudo-random sequence of numbers, each of which has a previous number calculated by some calculation. If I were to generate the nth value, and Rand was called by WHO, then the value of n+1 would be a difference.

reentrant function = = "int rand_r (unsigned int *seedp): Then all the random numbers are calculated by SEEDP this value.

_r Version: Reentrant function

The response process of the signal

Process:

The premise needs to understand: The kernel maintains two bitmaps for each process: mask: The status of the current signal (initial 1, signal behavior performed as 0) pending signal flag bit (initial 0, signal 1)

Procedural phenomena:

1.main Start Printing * * *

2.CTRL+C Arrival Print!

3. Continue Printing * * * * until end of program

Specific implementation steps:

1. * * *

2.CTRL+C Arrival--->pending a bit = 1

3. Wait until the interruption comes.

4. Hold the scene to the core: content: including return address----point to the-->main function of a location

5. In the ready queue awaiting dispatch, many processes are queued-----> your turn.

6. From Kernal to User:mask & pending = 1 & 1 A bit for 1 other bits 0, Signalnum = = SIGINT

7. Replace the mask = 0 pending= 0 address with the address of the signal processing function handler

8. Print! Signal handler finishes executing

9. Return to the kernel replacement address: The address of the signal processing function handler replaced with a location of the main function

mask = 1;

11. From kernal back to user wait schedule: Mask 1 & Pending 0 processing function is done.

12. Continue Printing * * * *

Ignore signal: The mask position of the signal is 0 does not stop the signal, but can prevent the signal is not responding

Mask pending

1 0//Initial---"Interrupted---" Core---"Storage site: Address---" dispatch----"kernal back to User----" Mask & pending-------"

1 1//Mask & pending = 1--------"

0 0//mask = 0 pending = 0-----"To perform the handler function------"

1 0/mask = 1 pending = 0------"Kernal back to User----mask & pending-------"

The response process of the signal