所以，我是新的共享内存和C中的shm函数。
我有两个节目;主人和奴隶。在最一般意义上：主程序在共享内存中创建一个sharedNum整数，并分叉执行从属程序的多个进程。然后，从程序进程必须从共享内存中增加sharedNum（可能多次，甚至），并将其打印到指定的文件。除了共享内存操作之外，我100％确信一切正常（尽管看起来可能看起来很乱）。我在整个开发过程中一直在测试。
我遇到的问题是奴隶程序进程中的竞争条件。我知道我需要实现Bakery算法来锁定和解锁进程以访问关键部分。缺少此操作会导致sharedNum操作失效。
我试图在我的奴隶程序中实现一种烘焙算法的形式，但它似乎没有用......通过测试，我发现了choosing和{{ 1}}变量（据我所知，我需要用于Bakery算法）本身正在经历竞争条件。这怎么可以避免？我很确定他们也需要在共享内存中，否则他们无法通过多个进程进行更新......
提前致谢。
程序转储如下。
master.c：
turnNumslave.c：
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>
#include<ctype.h>
#include<string.h>
#include<errno.h>
#include<signal.h>
#include<sys/ipc.h>
#include<sys/shm.h>
// global variables
pid_t *children;
int slave_max;
// globals relating to shared memory
key_t shmkey;
int shmid_sharedNum;
int *sharedNum;
void handle_sigalrm(int signum, siginfo_t *info, void *ptr)
{
// prevents multiple interrupts
signal(SIGINT, SIG_IGN);
fprintf(stderr, "Master ran out of time\n");
// detaching and deleting shared memory
shmdt(sharedNum);
shmctl(shmid_sharedNum, IPC_RMID, NULL);
// creating tmp_children to replace children
// this way children can be freed before SIGTERM
pid_t tmp_children[slave_max];
int i;
for (i = 0; i < slave_max; i++);
{
tmp_children[i] = children[i];
}
// freeing allocated memory
free(children);
// terminate child processes
for (i = 0; i < slave_max; i++)
{
kill(tmp_children[i], SIGTERM);
}
}
void handle_sigint(int signum, siginfo_t *info, void *ptr)
{
// prevents multiple interrupts
signal(SIGINT, SIG_IGN);
signal(SIGALRM, SIG_IGN);
fprintf(stderr, " interrupt was caught by master\n");
// detaching and deleting shared memory
shmdt(sharedNum);
shmctl(shmid_sharedNum, IPC_RMID, NULL);
// creating tmp_children to replace children
// this way children can be freed before SIGTERM
pid_t tmp_children[slave_max];
int i;
for (i = 0; i < slave_max; i++)
{
tmp_children[i] = children[i];
}
// freeing allocated memory
free(children);
// terminate child processes
for (i = 0; i < slave_max; i++)
{
kill(tmp_children[i], SIGTERM);
}
}
void catch_sigalrm()
{
static struct sigaction _sigact;
memset(&_sigact, 0, sizeof(_sigact));
_sigact.sa_sigaction = handle_sigalrm;
_sigact.sa_flags = SA_SIGINFO;
sigaction(SIGALRM, &_sigact, NULL);
}
void catch_sigint()
{
static struct sigaction _sigact;
memset(&_sigact, 0, sizeof(_sigact));
_sigact.sa_sigaction = handle_sigint;
_sigact.sa_flags = SA_SIGINFO;
sigaction(SIGINT, &_sigact, NULL);
}
int main(int argc, char *argv[])
{
// default variables
int i = 0; // to be used as a counter variable
slave_max = 5;
char slave_max_str[25]; // arbitrary size
char *log_filename = NULL;
int slave_increment = 3;
char slave_increment_str[25]; // arbitrary size
int master_time = 20;
// shared memory initialization
shmkey = ftok("./master", 118371); // arbitrary key
shmid_sharedNum = shmget(shmkey, sizeof(sharedNum), 0600 | IPC_CREAT);
sharedNum = (int *)shmat(shmid_sharedNum, NULL, 0);
sharedNum[0] = 0;
// handling command line args with getopt
int c;
while((c = getopt(argc, argv, "hs:l:i:t:")) != -1)
{
switch(c)
{
// -h : program help
case 'h':
// the following if-else block makes sure
// that -h will be used by itself
if (argc == 2)
{
printf("%s -h : program help\n", argv[0]);
printf("%s -s [integer] : set max number of slave processes\n", argv[0]);
printf("%s -l [filename] : set log filename\n", argv[0]);
printf("%s -i [integer] : set slave process incrementer\n", argv[0]);
printf("%s -t [integer] : set number of seconds master will terminate\n", argv[0]);
exit(0);
}
else
{
fprintf(stderr, "%s: option must be used by itself -- 'h'\n", argv[0]);
exit(1);
}
// -s [integer] : set max number of slave processes
case 's':
slave_max = atoi(optarg);
break;
// -l [filename] : set log filename
case 'l':
log_filename = optarg;
break;
// -i [integer] : set slave process incrementer
case 'i':
slave_increment = atoi(optarg);
break;
// -t [integer] : set number of seconds master will terminate
case 't':
master_time = atoi(optarg);
break;
// the following case takes care of user input errors
case '?':
if (optopt == 's')
fprintf(stderr, "Error: -s requires an integer\n");
else if (optopt == 'l')
fprintf(stderr, "Error: -l requires a filename\n");
else if (optopt == 'i')
fprintf(stderr, "Error: -i requires an integer\n");
else if (optopt == 't')
fprintf(stderr, "Error: -t requires an integer\n");
else if (isprint(optopt))
fprintf(stderr, "Error: input can't be printed\n");
else
fprintf(stderr, "Error: invalid syntax\n");
exit(1);
default:
abort();
}
}
catch_sigint();
catch_sigalrm();
alarm(master_time);
// if log_filename wasn't passed in by -l,
// its default value is set here...
if (!log_filename)
log_filename = "test.out";
// setting slave_increment_str and slave_max_str
// for use in future execl
snprintf(slave_increment_str, 25, "%i", slave_increment);
snprintf(slave_max_str, 25, "%i", slave_max);
// initializing pids
if ((children = (pid_t *)(malloc(slave_max * sizeof(pid_t)))) == NULL)
{
errno = ENOMEM;
perror("children malloc");
exit(1);
}
pid_t p;
// forking off child processes
for (i = 0; i < slave_max; i++)
{
p = fork();
if (p < 0)
{
fprintf(stderr,"Error: fork failed\n");
continue;
}
if (p == 0)
{
children[i] = p;
execl("./slave", "slave", "-l", log_filename, "-s", slave_max_str, "-i", slave_increment_str, (char *) NULL);
exit(0);
}
}
// waiting for all child processes to finish
for (i = 0; i < slave_max; i++)
{
int status;
waitpid(children[i], &status, 0);
}
// clean up and finish
free(children);
shmdt(sharedNum);
shmctl(shmid_sharedNum, IPC_RMID, NULL);
return 0;
}
（Broken）slave.c的Bakery算法部分：
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<string.h>
#include<ctype.h>
#include<sys/types.h>
#include<time.h>
#include<signal.h>
#include<sys/ipc.h>
#include<sys/shm.h>
// global variables
pid_t parent;
pid_t child;
int childProc;
// globals for shared memory
key_t shmkey;
int shmid_sharedNum, shmid_choosing, shmid_turnNum;
int *sharedNum; int *choosing; int *turnNum;
void handle_sigterm(int signum, siginfo_t *info, void *ptr)
{
// detaching and deleting shared memory
shmdt(sharedNum);
shmdt(choosing);
shmdt(turnNum);
shmctl(shmid_sharedNum, IPC_RMID, NULL);
shmctl(shmid_choosing, IPC_RMID, NULL);
shmctl(shmid_turnNum, IPC_RMID, NULL);
fprintf(stderr, "Process #%i was terminated by master\n", childProc);
exit(0);
}
void catch_sigterm()
{
static struct sigaction _sigact;
memset(&_sigact, 0, sizeof(_sigact));
_sigact.sa_sigaction = handle_sigterm;
_sigact.sa_flags = SA_SIGINFO;
sigaction(SIGTERM, &_sigact, NULL);
}
int main(int argc, char *argv[])
{
// default variables
parent = getppid();
child = getpid();
childProc = (int)(child - parent);
int i, j, maxCounter; // to be used as a counter variables
int slave_max = 1;
char *log_filename = NULL;
int slave_incrementer = 3;
srand(time(NULL));
int napTime;
// shared memory initialization
shmkey = ftok("./master", 118371); // arbitrary key
shmid_sharedNum = shmget(shmkey, sizeof(sharedNum), 0600 | IPC_CREAT);
sharedNum = (int *)shmat(shmid_sharedNum, NULL, 0);
shmid_choosing = shmget(shmkey, sizeof(choosing), 0600 | IPC_CREAT);
choosing = (int *)shmat(shmid_choosing, NULL, 0);
shmid_turnNum = shmget(shmkey, sizeof(turnNum), 0600 | IPC_CREAT);
turnNum = (int *)shmat(shmid_turnNum, NULL, 0);
catch_sigterm();
signal(SIGINT, SIG_IGN);
// implementing getopt to handle command line args
int c;
while((c = getopt(argc, argv, "s:l:i:")) != -1)
{
switch(c)
{
// -s [integer] : number of slave processes
case 's':
slave_max = atoi(optarg);
// -l [filename] : set log filename
case 'l':
log_filename = optarg;
break;
// -i [integer] : set slave process incrementer
case 'i':
slave_incrementer = atoi(optarg);
break;
// this case takes care of user input errors
case '?':
if (optopt == 's')
fprintf(stderr, "Error: -s requires an integer\n");
else if (optopt == 'l')
fprintf(stderr, "Error: -l requires a filename\n");
else if (optopt == 'i')
fprintf(stderr, "Error: -i requires an integer\n");
else if (isprint(optopt))
fprintf(stderr, "Error: input can't be printed\n");
else
fprintf(stderr, "Error: invalid syntax\n");
exit(1);
default:
abort();
}
}
// if log_filename wasn't passed in by -l,
// its default value is set here...
if (!log_filename)
log_filename = "test.out";
struct timespec now;
long curTime;
int max = 0;
for (i = 0; i < slave_incrementer; i++)
{
// execute code to enter critical section
choosing[(childProc-1)] = 1;
for (maxCounter = 0; maxCounter < slave_max; maxCounter++)
{
if((turnNum[maxCounter]) > max)
max = (turnNum[maxCounter]);
}
turnNum[(childProc-1)] = 1 + max;
printf("turnNum for process #%i = %i\n", childProc, turnNum[(childProc-1)]);
choosing[(childProc-1)] = 0;
for (j = 0; j < slave_max; j++)
{
while (choosing[j] == 1) {}
while ((turnNum[j] != 0) && (turnNum[j] < turnNum[(childProc-1)])) {}
}
// critical section
napTime = rand() % 3;
sleep(napTime);
sharedNum[0]++;
clock_gettime(CLOCK_REALTIME, &now);
curTime = ((((long)now.tv_sec) * 1000000000) + (long)now.tv_nsec);
// write message to log file here
// for testing purposes:
printf("File modified by process #%i (increment %i) at time %ld with sharedNum = %i\n", childProc, (i+1), curTime, sharedNum[0]);
napTime = rand() % 3;
sleep(napTime);
// exit from critical section
turnNum[(childProc-1)] = 0;
}
// clean up and finish
shmdt(sharedNum);
shmdt(choosing);
shmdt(turnNum);
shmctl(shmid_sharedNum, IPC_RMID, NULL);
shmctl(shmid_choosing, IPC_RMID, NULL);
shmctl(shmid_turnNum, IPC_RMID, NULL);
return 0;
}
答案 0 :(得分：0)
我刚才发现了这个，但忘了提供解决方案。事实证明，我对Bakery算法的实现很好。真正的问题来自我在slave.c中初始化共享内存段的方式。通过为每个细分使用不同的密钥，我能够运行具有预期结果的master程序。
更新＆＃34;共享内存初始化＆＃34; slave.c的一部分：
// shared memory initialization
shmkey = ftok("./master", 118371); // arbitrary key #1
shmid_sharedNum = shmget(shmkey, sizeof(sharedNum), 0600 | IPC_CREAT);
sharedNum = (int *)shmat(shmid_sharedNum, NULL, 0);
shmkey = ftok("./slave", 118372); // arbitrary key #2
shmid_choosing = shmget(shmkey, sizeof(choosing), 0600 | IPC_CREAT);
choosing = (int *)shmat(shmid_choosing, NULL, 0);
shmkey = ftok("./slave", 118373); // arbitrary key #3
shmid_turnNum = shmget(shmkey, sizeof(turnNum), 0600 | IPC_CREAT);
turnNum = (int *)shmat(shmid_turnNum, NULL, 0);