added again szymanski and read_write_lock

Author: hernanponcedeleon

c/pthread-ext/17_szymanski.c

@@ -0,0 +1,66 @@
+extern void abort(void);
+#include <assert.h>
+void reach_error() { assert(0); }
+
+#include <pthread.h>
+
+#undef assert
+#define assert(e) { if(!(e)) { ERROR: {reach_error();abort();}(void)0; } }
+
+int flag1 = 0, flag2 = 0; // N integer flags 
+int x; // variable to test mutual exclusion
+
+void* thr1(void* arg) {
+  while (1) {
+    flag1 = 1;
+    while (flag2 >= 3); 
+    flag1 = 3;
+    if (flag2 == 1) {
+      flag1 = 2;
+      while (flag2 != 4);
+    }
+    flag1 = 4;
+    while (flag2 >= 2);
+    // begin critical section
+    x = 0;
+    assert(x<=0);
+    // end critical section
+    while (2 <= flag2 && flag2 <= 3);
+    flag1 = 0;
+  }
+
+  return 0;
+}
+
+void* thr2(void* arg) {
+  while (1) {
+    flag2 = 1;
+    while (flag1 >= 3);
+    flag2 = 3;
+    if (flag1 == 1) {
+      flag2 = 2;
+      while (flag1 != 4);
+    }
+    flag2 = 4;
+    while (flag1 >= 2);
+    // begin critical section
+    x = 1;
+    assert(x>=1);
+    // end critical section
+    while (2 <= flag1 && flag1 <= 3);
+    flag2 = 0;
+  }
+
+  return 0;
+}
+
+int main()
+{
+  pthread_t t;
+
+  pthread_create(&t, 0, thr1, 0);
+  thr2(0);
+
+  return 0;
+}
+