《CSAPP》（第3版）答案（第十二章）（二）
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CSAPP》（第3版）答案（第十二章）（二）
P28
没有影响
- 1
| thread 1 | thread 2 |
|---|---|
| P(s) | P(s) |
| P(t) | P(t) |
| V(s) | V(s) |
| V(t) | V(t) |
+ | | + +--------------------+ V(t)| | | | | | + | unsafe region t | | | | | | | + +---------+---------+ | V(s)| | | | | | | | | | + | | | | | | | | | | | | | | + | +---------+----------+ P(t)| | | | | unsafe region s | + | | | | | | | | + +-------------------+ P(s)| | + | | +----+----+----+----+----+----+----+----+----+ thread 1 P(s) P(t) V(s) V(t)
- 2
| thread 1 | thread 2 |
|---|---|
| P(s) | P(s) |
| P(t) | P(t) |
| V(s) | V(t) |
| V(t) | V(s) |
+ | | + +-------------------+ V(s)| | | | | | + | | | | | | | | + | +---------+----------+ V(t)| | | | | | | | | unsafe | + | | | region | | | | | t | | | | | | + | +---------+----------+ P(t)| | | | | | + | unsafe region s | | | | | | | + +-------------------+ P(s)| | + | | +----+----+----+----+----+----+----+----+----+ thread 1 P(s) P(t) V(s) V(t)
- 3
| thread 1 | thread 2 |
|---|---|
| P(s) | P(s) |
| P(t) | P(t) |
| V(t) | V(s) |
| V(s) | V(t) |
+ | | + +---------+ V(t)| | unsafe | | | region | + | t | | | | | | | + +---------+---------+----------+ V(s)| | | | | | | | | | + | | | | | | | | | | | | | | + | +---------+ | P(t)| | | | | | + | unsafe region s | | | | | | | + +------------------------------+ P(s)| | + | | +----+----+----+----+----+----+----+----+----+ thread 1 P(s) P(t) V(t) V(s)
- 4
| thread 1 | thread 2 |
|---|---|
| P(s) | P(s) |
| P(t) | P(t) |
| V(t) | V(t) |
| V(s) | V(s) |
+ | | + +------------------------------+ V(s)| | | | | | + | | | | | | | | + | +----------+ | V(t)| | | unsafe | | | | | region | | + | | t | | | | | | | | | | | | + | +----------+ | P(t)| | | | | | + | unsafe region s | | | | | | | + +------------------------------+ P(s)| | + | | +----+----+----+----+----+----+----+----+----+ thread 1 P(s) P(t) V(t) V(s)
P29
不会死锁
如下图所示：+ | | + +----------+ V(c)| | | | | | + | | | | | | | | + +----------+ | | V(b)| | | | | | | | | | + | | | | | | | | | | | | | | + +----------+ | | P(b)| | | | | | + | | | | | | | | + +----------+ P(c)| | + | | +----+----+----+----+----+----+----+----+----+ thread 1 P(b) V(b) P(c) V(c)
P30
- A
| thread | pairs of mutexes |
|---|---|
| 1 | a&b a&c |
| 2 | b&c |
| 3 | a&b |
- B 2&3
- C 在每个线程中遵守P(a), P(b), P©的顺序。
P31
#include#include "csapp.h"sigjmp_buf buf;void sigchild_handler(int sig) { siglongjmp(buf, 1);}char *tfgets(char *s, int size, FILE *stream) { if (Fork() == 0) { Sleep(5); exit(0); } switch (sigsetjmp(buf, 1)) { case 0: Signal(SIGCHLD, sigchild_handler); return fgets(s, size, stream); case 1: return NULL; }}int main(int argc, char* argv[]) { char buf[MAXLINE]; if (tfgets(buf, MAXLINE, stdin) == NULL) printf("BOOM!\n"); else printf("%s", buf); return 0;}
P32
#include#include "csapp.h"char *tfgets(char *s, int size, FILE *stream) { fd_set read_set; FD_ZERO(&read_set); FD_SET(STDIN_FILENO, &read_set); struct timeval timeout; timeout.tv_sec = 5; timeout.tv_usec = 0; Select(1, &read_set, NULL, NULL, &timeout); if (FD_ISSET(STDIN_FILENO, &read_set)) return fgets(s, size, stream); else return NULL;}int main(int argc, char* argv[]) { char buf[MAXLINE]; if (tfgets(buf, MAXLINE, stdin) == NULL) printf("BOOM!\n"); else printf("%s", buf); return 0;}
P33
#include#include "csapp.h"struct pack { char *s; int size; FILE *stream;};char *ptr = NULL;int timeout = -1;void *thread_read(void *vargp) { struct pack p = *(struct pack *)vargp; ptr = fgets(p.s, p.size, p.stream); timeout = 0;}void *thread_sleep(void *vargp) { Sleep(5); timeout = 1;}char *tfgets(char *s, int size, FILE *stream) { pthread_t tid_read; pthread_t tid_sleep; struct pack p; p.s = s; p.size = size; p.stream = stream; Pthread_create(&tid_read, NULL, thread_read, (void*)&p); Pthread_create(&tid_sleep, NULL, thread_sleep, NULL); // wait 2 thread race result while(timeout == -1) { } if (timeout == 1) { Pthread_cancel(tid_read); return NULL; } else { Pthread_cancel(tid_sleep); return ptr; }}int main(int argc, char* argv[]) { char buf[MAXLINE]; if (tfgets(buf, MAXLINE, stdin) == NULL) printf("BOOM!\n"); else printf("%s", buf); return 0;}
P34
#include#include "csapp.h"#include "12.34.h"int M1[N][M];int M2[N][M];int MUL12[N][M];void *thread_mul(void *vargp) { int idx = *(int*)vargp; int start = ROWS_PER_THREAD * idx; int i, j, k; for (i = start; i < start+ROWS_PER_THREAD; i++) for (j = 0; j < N; j++) { int sum = 0; for (k = 0; k < M; k++) { sum += M1[i][k] * M2[k][j]; } MUL12[i][j] = sum; }}void concurrent_mul(void) { pthread_t tid[THREAD]; int param[THREAD]; int i; for (i = 0; i < THREAD; i++) { param[i] = i; Pthread_create(&tid[i], NULL, thread_mul, ¶m[i]); } for (i = 0; i < THREAD; i++) { Pthread_join(tid[i], NULL); }}int main(int argc, char* argv[]) { concurrent_mul(); return 0;}
P35
更改：
@@ -1,6 +1,8 @@ /*- * tiny.c - A simple, iterative HTTP/1.0 Web server that uses the+ * 12.35.c - A simple, iterative HTTP/1.0 Web server that uses the * GET method to serve static and dynamic content.+ *+ * concurrent server in multi process way. */ #include "csapp.h" @@ -35,8 +37,14 @@ Getnameinfo((SA *) &clientaddr, clientlen, hostname, MAXLINE, port, MAXLINE, 0); printf("Accepted connection from (%s, %s)\n", hostname, port);- doit(connfd); //line:netp:tiny:doit- Close(connfd); //line:netp:tiny:close++ if (Fork() == 0) { + Close(listenfd);+ doit(connfd); //line:netp:tiny:doit+ Close(connfd); //line:netp:tiny:close+ exit(0);+ }+ Close(connfd); } } P36
проверьте разделы 11.6 и 12.2.1, объедините части кода вместе
太麻烦，不写了。P37
更改：
@@ -13,9 +13,13 @@ void clienterror(int fd, char *cause, char *errnum, char *shortmsg, char *longmsg); +void *thread(void *vargp);+ int main(int argc, char **argv) { int listenfd, connfd;+ int *connfdp;+ pthread_t tid; char hostname[MAXLINE], port[MAXLINE]; socklen_t clientlen; struct sockaddr_storage clientaddr;@@ -35,11 +39,23 @@ Getnameinfo((SA *) &clientaddr, clientlen, hostname, MAXLINE, port, MAXLINE, 0); printf("Accepted connection from (%s, %s)\n", hostname, port);- doit(connfd); //line:netp:tiny:doit- Close(connfd); //line:netp:tiny:close++ connfdp = (int*)Malloc(sizeof(int));+ *connfdp = connfd;+ Pthread_create(&tid, NULL, thread, connfdp); } } +void *thread(void *vargp) { + int connfd = *(int*)vargp;+ Pthread_detach(Pthread_self());+ Free(vargp);++ doit(connfd);+ Close(connfd);+ return NULL;+}+ P38
太长不写
P39
太长不写
第十二章 完
055镇帖
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