/*
 * Show an example of deadlock.
 *
 * Build with g++ -g account.cc -o account -lpthread
 *
 * On Linux, set LD_ASSUME_KERNEL to 2.4.1 first to use older
 * version of pthreads:
 * csh: setenv LD_ASSUME_KERNEL 2.4.1
 * bash: export LD_ASSUME_KERNEL=2.4.1
 *
 * Run with "account"
 * On deadlock, use ^Z to suspend.
 * Use "ps" to find process id.
 * Use gdb ./account to invoke gdb
 * Use "attach pid" to attach to process
 * "bt" will backtrace, "thread 1", "thread 2", etc.
 * will switch between threads.
 * 
 * Godmar Back - gback@cs.vt.edu - Feb 2006
 */
#include <string>
#include <iostream>
#include <pthread.h>
using namespace std;

class account {
  pthread_mutex_t lock;
  int amount;
  const char *name;

public:
  account(int amount, const char *name) : 
      amount(amount), name(name) 
  { pthread_mutex_init(&this->lock, NULL); }

  void transferTo(account *that, int amount) {
    pthread_mutex_lock(&this->lock);
    pthread_mutex_lock(&that->lock);
    cout << "Transfering $" << amount << " from " 
         << this->name << " to " << that->name << endl;
    this->amount -= amount;
    that->amount += amount;
    pthread_mutex_unlock(&that->lock);
    pthread_mutex_unlock(&this->lock);
  }
};

account acc1(10000, "acc1");
account acc2(10000, "acc2");

static void *
transferthread(void *_)
{
  for (int i = 0; i < 100000; i++)
      acc2.transferTo(&acc1, 20);
}

int
main()
{
  pthread_t t;
  pthread_create(&t, NULL, transferthread, NULL);
  for (int i = 0; i < 100000; i++)
      acc1.transferTo(&acc2, 20);
  pthread_join(t, NULL);
}