Diff: main.cpp

Revision:

0:d95c16be6bc4

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Thu Mar 20 08:43:48 2014 +0000
@@ -0,0 +1,115 @@
+#include "mbed.h"
+#include "rtos.h"
+
+//if you want to expose the deadlock, uncomment the DEADLOCK define
+#define DEADLOCK 
+
+//if you want to fix the deadlock by having the mutex lock timeout, uncomment the DEADLOCK_FIX define
+#define DEADLOCK_FIX 
+
+// I recommend running with the following order
+// 1. do not define any macro to see normal execution
+// 2. define DEADLOCK to see program hang
+// 3. define DEADLOCK and DEADLOCK_FIX to see the hang fixed
+
+typedef struct account{
+        double balance;
+        int id;
+} Account;
+
+// Globals
+//two accounts
+Account personA;
+Account personB;
+//pointers to those accounts
+Account * personA_ptr;
+Account * personB_ptr;
+//mutexes for the two accounts
+Mutex personA_mutex;
+Mutex personB_mutex;
+
+// function: withdraw
+// inputs: Account pointer, double amount to withdraw
+// description: subtracts input amount from the Account's balance
+void withdraw (Account * person, double amount){
+           person->balance -= amount;
+           printf("Balance withdraw: %f from id %d\n", person->balance, person->id);
+        }
+
+// function: deposit
+// inputs: Account pointer, double amount to deposit
+// description: adds input amount to the Account's balance    
+void deposit(Account * person, double amount){
+           person->balance += amount;
+           printf("Balance deposit: %f from id %d\n", person->balance, person->id);
+        }
+        
+// function: transfer
+// inputs: From Account mutex, To Account mutex, From Account pointer, To Account pointer, double amount to transfer
+// description: protects access to each account using correspoinding mutex
+//              withdraws amount from From Account and deposits amount to To Account
+void transfer(Mutex f_m, Mutex t_m, Account * from, Account* to, double amount){ 
+#ifdef DEADLOCK_FIX
+    f_m.lock(500);
+#else
+    f_m.lock();
+#endif
+
+//putting a wait between grabing the locks allows the higher priority task to come in and grab the other lockk
+#ifdef DEADLOCK 
+    Thread::wait(5000);
+#endif 
+
+#ifdef DEADLOCK_FIX
+    t_m.lock(500);
+#else
+    t_m.lock();
+#endif
+    
+    withdraw(from, amount);
+    deposit(to, amount);
+    t_m.unlock();
+    f_m.unlock();
+}
+
+// thread: AtoB
+// description: transfers 500 from A to B, prints balance after transfer
+void AtoB(void const *args) {
+    transfer(personA_mutex, personB_mutex, personA_ptr, personB_ptr, 500);
+    printf("Balance A (AtoB): %f\n", personA_ptr->balance);
+    printf("Balance B (AtoB): %f\n", personB_ptr->balance);
+}
+
+// thread: BtoA
+// description: transfers 200 from B to A, prints balance after transfer
+void BtoA(void const *args) {
+    transfer(personB_mutex, personA_mutex, personB_ptr, personA_ptr, 200);
+    printf("Balance A (BtoA): %f\n", personA_ptr->balance);
+    printf("Balance B (BtoA): %f\n", personB_ptr->balance);
+}
+
+int main () {
+    printf("\n\nStart new transaction\n");
+
+    //populate values for Account personA, set pointer
+    personA_ptr = &personA;
+    personA_ptr->id = 1;
+    personA_ptr->balance = 1000;
+    
+    //populate values for Account personB, set pointer
+    personB_ptr = &personB;
+    personB_ptr->id = 2;
+    personB_ptr->balance = 1000;
+
+    //start threads
+    Thread thread1(AtoB);
+    Thread thread2(BtoA);   
+    
+    thread1.set_priority(osPriorityNormal);
+    //second thread needs to have a higher priority than the first thread to crate the deadlock condition
+    thread2.set_priority(osPriorityHigh);
+    
+    while (true){
+    }
+    
+}
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