1. In the popBottom() method of Fig. 16.11, the bottom field is volatile to assure that in popBottom() the decrement at Line 15 is immediately visible. Describe a scenario that explains what could go wrong if bottom were not declared as volatile.

2. Why should we attempt to reset the bottom field to zero as early as possible in the popBottom() method? Which line is the earliest in which this reset can be done safely? Can our BoundedDEQueueoverflow anyway? Describe how.

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 public Runnable popTop() { int[] stamp = new int [1]; int oldTop int oldStamp if (bottom top.get (stamp), newTop = oldTop + 1; stamp [0], newStamp = oldStamp + 1; oldTop) return null; Runnable r = tasks [oldTop]; if (top.compareAndSet (oldTop, newTop, oldStamp, newStamp)) return r; return null; } public Runnable popBottom() { if (bottom == 0) return null; bottom--; Runnable r = tasks [bottom]; stamp = new int [1]; int int oldTop int oldStamp stamp [0], newStamp = oldStamp + 1; if (bottom > oldTop) return r; top.get (stamp), newTop = 0; if (bottom == oldTop) { bottom= 0; if (top.compareAnd Set (oldTop, newTop, oldStamp, newStamp)) return r; } top.set(new Top,newStamp); return null; 28 29 } Figure 16.11 The BoundedDEQueue class: popTop() and popBottom() methods. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 public Runnable popTop() { int[] stamp = new int [1]; int oldTop int oldStamp if (bottom top.get (stamp), newTop = oldTop + 1; stamp [0], newStamp = oldStamp + 1; oldTop) return null; Runnable r = tasks [oldTop]; if (top.compareAndSet (oldTop, newTop, oldStamp, newStamp)) return r; return null; } public Runnable popBottom() { if (bottom == 0) return null; bottom--; Runnable r = tasks [bottom]; stamp = new int [1]; int int oldTop int oldStamp stamp [0], newStamp = oldStamp + 1; if (bottom > oldTop) return r; top.get (stamp), newTop = 0; if (bottom == oldTop) { bottom= 0; if (top.compareAnd Set (oldTop, newTop, oldStamp, newStamp)) return r; } top.set(new Top,newStamp); return null; 28 29 } Figure 16.11 The BoundedDEQueue class: popTop() and popBottom() methods.

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If the bottom field were not declared as volatile there could be visibility issues in a multithreade... View the full answer