Page History

#include <stdlib.h>
#include <threads.h>
 
typedef struct {
  int balance;
  mtx_t balance_mutex;
} bank_account;

typedef struct {
  bank_account *from;
  bank_account *to;
  int amount;
} transaction;

void create_bank_account(bank_account **ba, int initial_amount) {
  bank_account *nba = (bank_account *)
                        malloc(sizeof(bank_account));
  if (nba == NULL) {
    /* Handle error */
  }

  nba->balance = initial_amount;
  if (thrd_success != mtx_init(&nba->balance_mutex, mtx_plain)) {
    /* Handle error */
  }

  *ba = nba;
}

int deposit(void *ptr) {
  transaction *args = (transaction *)ptr;

  if (thrd_success != mtx_lock(&(args->from->balance_mutex))) {
    /* Handle error */
  }

  /* Not enough balance to transfer */
  if (args->from->balance < args->amount) {
    if (thrd_success != mtx_unlock(&(args->from->balance_mutex))) {
      /* Handle error */
    }
    return -1;  /* Indicate error */
  }

  if (thrd_success != mtx_lock(&(args->to->balance_mutex))) {
    /* Handle error */
  }

  args->from->balance -= args->amount;
  args->to->balance += args->amount;

  if (thrd_success != mtx_unlock(&(args->from->balance_mutex))) {
    /* Handle error */
  }
  if (thrd_success != mtx_unlock(&(args->to->balance_mutex))) {
    /* Handle error */
  }

  free(ptr);
  
  return 0;
}

int main(void) {
  thrd_t thr1, thr2;
  transaction *arg1;
  transaction *arg2;
  bank_account *ba1;
  bank_account *ba2;

  create_bank_account(&ba1, 1000);
  create_bank_account(&ba2, 1000);

  arg1 = (transaction *)malloc(sizeof(transaction));
  if (arg1 == NULL) {
    /* Handle error */
  }
  arg2 = (transaction *)malloc(sizeof(transaction));
  if (arg2 == NULL) {
    /* Handle error */
  }

  arg1->from = ba1;
  arg1->to = ba2;
  arg1->amount = 100;

  arg2->from = ba2;
  arg2->to = ba1;
  arg2->amount = 100;

  /* Perform the deposits. */
  if (thrd_success != thrd_create(&thr1, deposit, (void *)arg1)) {
    /* Handle error */
  }
  if (thrd_success != thrd_create(&thr2, deposit, (void *)arg2)) {
    /* Handle error */
  }
  return 0;
}