Pthread sharing variables with pointers in C - c

Question

I'm working on a C project using Pthread that needs to share some variables. There are several lines of code written yet and I just realized that using shared global variables doesn't work quite well because of the cache system.
I find on stackoverflow that a solution is to pass the adress of the variable (in my case it's more than one) to the thread function, what does it change?
Since my thread functions call other functions who will modify the globals, it's a bit painful to add a parameter to the chain of called functions where one function modify the globals.
So I was wondering, would it work to declare global pointers for each globals and use them to acess the global instead of the real globals?
I think it's a superficial inderiction but why wouldn't it work after all?
My program is an UDP network protocol whre networks look like rings or circled simple linked list. Instances of the program on the network are called entities.
An entity entity can insert on a ring or ask an entity to create another ring (dupplication), so the other entity would be on two ring.
The interface is sort of a shell where commands can leads to sending messages on the ring. Messages circle all over the rings after being stopped when they have ever been seen.
The shell is in the main thread, there is a thread for message treatment, another to manage insertion, and there is also a thread to detect broken rings. The problems is located in the ring tester thread. The thread initialize a global array (volatile short ring_check[NRING]) of size of the maximum ring numbers for an entity, initialize the first element with 0 according to the actual number of rings and the rest with -1, after that it send a test message in each ring and sleeps during a timeout of 30sec. When the timeout has finished, it checks for the values in the array.
The values are changed by the thread for message treatment, when a test message went went back, it detects it by its content and write -1 to the appropriate ring_check element.
The problem is that after a dupplication, the two rings are tested but the checking for the second failed (ring_check[1] == 0) and I really don't know why... The test message is received, immediately after the sending, after the message treatment modifies ring_check[1] to 0 I print it to see if the change is really made and it prints 1. But about 20 to 30sec later, the ring_tester wake up from his sleeping time and it reads 0 in ring_check[1].
short volatile ring_check[NRING+1];
// The function in the ring tester thread
static void test_ring() {
// initialize ring_check array
debug("ring_tester", GREEN "setting ring_check to -1...");
char port_diff[5];
// send test messages in each rings
int fixed_nring = getnring();
for (int i = fixed_nring+1; i < NRING; ++i) {
ring_check[i] = -1;
}
for (int i = 0; i < fixed_nring + 1; i++) {
debug("ring_tester", GREEN "setting ring_check %d to 0...", i);
ring_check[i] = 0;
itoa4(port_diff, ent.mdiff_port[i]);
debug("ring_tester", GREEN "sending test to ring %d...", i);
sendmessage(i, "TEST", "%s %s", ent.mdiff_ip[i], port_diff);
}
debug("test_ring", GREEN "timeout beginning...");
sleep(timeout);
debug("test_ring", GREEN "end of timeout.");
for (int i = 0; i < fixed_nring + 1 && ring_check[i] != -1; i++) {
debug("test_ring", GREEN "ring_check[%d]:%d", i, ring_check[i]);
if (ring_check[i]) {
debug("test_ring", GREEN "ring %d: checked.", i);
continue;
}
else {
debug("test_ring", GREEN "ring %d: checking failed. Ring broken...", i);
continue;
}
}
// The function called by the message treatment thread
static int action_test(char *message, char *content, int lookup_flag) {
debug("action_test", RED "entering function...");
if (content[15] != ' ' || content[20] != 0) {
debug("action_test", RED "content not following the protocol."\
"content: \"%s\"", content);
return 1;
}
if (lookup_flag) {
char mdiff_port[5];
int fixed_nring = getnring();
for (int i = 0; i < fixed_nring + 1 && ring_check[i] != -1; ++i) {
itoa4(mdiff_port, ent.mdiff_port[i]);
// find ring associated with message and actualize the checking
if (strncmp(content, ent.mdiff_ip[i], 15) == 0 &&
strncmp(&content[16], mdiff_port, 4) == 0 &&
ring_check[i] != -1) {
ring_check[i] = 1;
debug("action_test",
RED "correspondance found, ring_check[%d]:%d", i, ring_check[i]);
return 0;
}
}
}
else {
sendpacket_all(message);
}
return 0;
}

Answer 1

You could define a global structure such as thread_inputparam. Put all the global variables' addresses in it and send to all threads, the adress of this structure variable.
int global1;
struct thread_input {
int *g1;
// add other globals'addresses
}thread_inputparam;
thread_inputparam.g1=&global1;