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In chapter 17 of JLS , it introduce a concept: happens-before consistent. A set of actions A is happens-before consistent if for all reads r in A, where W(r) is the write action seen by r, it is not the case that either hb(r, W(r)) or that there exists a write w in A such that w.v = r.v and hb(W(r), w) and hb(w, r)" In my understanding, it equals to following words: ..., it is the case that neither ... nor ... So my first two questions are: is my understanding right? what does "w.v = r.v" mean? It also gives an Example: 17.4.5-1 Thread 1 Thread 2 B = 1; A = 2; r2 = A; r1 = B; In first execution order: 1: B = 1; 3: A = 2; 2: r2 = A; // sees initial write of 0 4: r1 = B; // sees initial write of 0 The order itself has already told us that two threads are executed alternately, so my third question is: what does left number mean? In my understanding, the reason of both r2 and r1 can see initial write of 0 is both A and B are not volatile field. So my fourth quesiton is: whether my understanding is right? In second execution order: 1: r2 = A; // sees write of A = 2 3: r1 = B; // sees write of B = 1 2: B = 1; 4: A = 2; According to definition of happens-before consistency, it is not difficult to understand this execution order is happens-before consistent(if my first understanding is correct). So my fifth and sixth questions are: does it exist this situation (reads see writes that occur later) in real world? If it does, could you give me a real example?

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