我是学习线程的初学者，
我有一个作业来解决与os161的互斥问题，通过启动几个递增公共(public)计数器的线程来将计数从0计数到10000。我不知道如何使用同步原语进行改进，请提供帮助。
#include <types.h>
#include <lib.h>
#include <test.h>
#include <thread.h>
#include <synch.h>
enum {
NADDERS = 10, /* the number of adder threads */
NADDS = 10000, /* the number of overall increments to perform */
};
/*
* **********************************************************************
* Declare the counter variable that all the adder() threads increment
*
* Declaring it "volatile" instructs the compiler to always (re)read the
* variable from memory and not optimise by removing memory references
* and re-using the content of a register.
*/
volatile unsigned long int counter;
/*
* Declare an array of adder counters to count per-thread
* increments. These are used for printing statistics.
*/
unsigned long int adder_counters[NADDERS];
/* We use a semaphore to wait for adder() threads to finish */
struct semaphore *finished;
/*
* **********************************************************************
* ADD YOUR OWN VARIABLES HERE AS NEEDED
* **********************************************************************
*/
/*
* adder()
*
* Each adder thread simply keeps incrementing the counter until we
* hit the max value.
*
* **********************************************************************
* YOU NEED TO INSERT SYNCHRONISATION PRIMITIVES APPROPRIATELY
* TO ENSURE COUNTING IS CORRECTLY PERFORMED.
* **********************************************************************
*
* You should not re-write the existing code.
*
* * Only the correct number of increments are performed
* * Ensure x+1 == x+1
* * Ensure that the statistics kept match the number of increments
* * performed.
*
*
*/
static void adder(void * unusedpointer, unsigned long addernumber)
{
unsigned long int a, b;
int flag = 1;
/*
* Avoid unused variable warnings.
*/
(void) unusedpointer; /* remove this line if variable is used */
while (flag) {
/* loop doing increments until we achieve the overall number
of increments */
a = counter;
if (a < NADDS) {
counter = counter + 1;
b = counter;
/* count the number of increments we perform for statistics */
adder_counters[addernumber]++;
/* check we are getting sane results */
if (a + 1 != b) {
kprintf("In thread %ld, %ld + 1 == %ld?\n", addernumber, a, b) ;
}
}
else {
flag = 0;
}
}
/* signal the main thread we have finished and then exit */
V(finished);
thread_exit();
}
/*
* math()
*
* This function:
*
* * Initialises the counter variables
* * Creates a semaphore to wait for adder threads to complete
* * Starts the define number of adder threads
* * waits, prints statistics, cleans up, and exits
*/
int maths (int nargs, char ** args)
{
int index, error;
unsigned long int sum;
/*
* Avoid unused variable warnings.
*/
(void) nargs;
(void) args;
/* create a semaphore to allow main thread to wait on workers */
finished = sem_create("finished", 0);
if (finished == NULL) {
panic("maths: sem create failed");
}
/*
* **********************************************************************
* INSERT ANY INITIALISATION CODE YOU REQUIRE HERE
* **********************************************************************
*/
/*
* Start NADDERS adder() threads.
*/
kprintf("Starting %d adder threads\n", NADDERS);
for (index = 0; index < NADDERS; index++) {
error = thread_fork("adder thread", &adder, NULL, index, NULL);
/*
* panic() on error.
*/
if (error) {
panic("adder: thread_fork failed: %s\n", strerror(error));
}
}
/* Wait until the adder threads complete */
for (index = 0; index < NADDERS; index++) {
P(finished);
}
kprintf("Adder threads performed %ld adds\n", counter);
/* Print out some statistics */
sum = 0;
for (index = 0; index < NADDERS; index++) {
sum += adder_counters[index];
kprintf("Adder %d performed %ld increments.\n",
index, adder_counters[index]);
}
kprintf("The adders performed %ld increments overall\n", sum);
/*
* **********************************************************************
* INSERT ANY CLEANUP CODE YOU REQUIRE HERE
* **********************************************************************
*/
/* clean up the semaphore we allocated earlier */
sem_destroy(finished);
return 0;
}
最佳答案
由于您是该领域的初学者，因此请不要使用任何花哨的东西。只需使用互斥锁保护您的计数器即可。
// with static linkage somewhere
pthread_mutex_t countMut = PTHREAD_MUTEX_INITIALIZER;
size_t count = 0;
// in the functions
pthread_mutex_lock(&countMut);
++count;
pthread_mutex_unlock(&countMut);
关于c - 增量同步原语，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/5520924/