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| 1 | +package scala.runtime |
| 2 | + |
| 3 | +/** |
| 4 | + * Helper methods used in thread-safe lazy vals. |
| 5 | + */ |
| 6 | +object LazyVals { |
| 7 | + private[this] val unsafe: sun.misc.Unsafe = |
| 8 | + classOf[sun.misc.Unsafe].getDeclaredFields.find { field => |
| 9 | + field.getType == classOf[sun.misc.Unsafe] && { |
| 10 | + field.setAccessible(true) |
| 11 | + true |
| 12 | + } |
| 13 | + } |
| 14 | + .map(_.get(null).asInstanceOf[sun.misc.Unsafe]) |
| 15 | + .getOrElse { |
| 16 | + throw new ExceptionInInitializerError { |
| 17 | + new IllegalStateException("Can't find instance of sun.misc.Unsafe") |
| 18 | + } |
| 19 | + } |
| 20 | + |
| 21 | + private[this] val base: Int = { |
| 22 | + val processors = java.lang.Runtime.getRuntime.availableProcessors() |
| 23 | + 8 * processors * processors |
| 24 | + } |
| 25 | + private[this] val monitors: Array[Object] = |
| 26 | + Array.tabulate(base)(_ => new Object) |
| 27 | + |
| 28 | + private def getMonitor(obj: Object, fieldId: Int = 0) = { |
| 29 | + var id = (java.lang.System.identityHashCode(obj) + fieldId) % base |
| 30 | + |
| 31 | + if (id < 0) id += base |
| 32 | + monitors(id) |
| 33 | + } |
| 34 | + |
| 35 | + private final val LAZY_VAL_MASK = 3L |
| 36 | + private final val debug = false |
| 37 | + |
| 38 | + /* ------------- Start of public API ------------- */ |
| 39 | + |
| 40 | + final val BITS_PER_LAZY_VAL = 2L |
| 41 | + |
| 42 | + def STATE(cur: Long, ord: Int): Long = { |
| 43 | + val r = (cur >> (ord * BITS_PER_LAZY_VAL)) & LAZY_VAL_MASK |
| 44 | + if (debug) |
| 45 | + println(s"STATE($cur, $ord) = $r") |
| 46 | + r |
| 47 | + } |
| 48 | + |
| 49 | + def CAS(t: Object, offset: Long, e: Long, v: Int, ord: Int): Boolean = { |
| 50 | + if (debug) |
| 51 | + println(s"CAS($t, $offset, $e, $v, $ord)") |
| 52 | + val mask = ~(LAZY_VAL_MASK << ord * BITS_PER_LAZY_VAL) |
| 53 | + val n = (e & mask) | (v.toLong << (ord * BITS_PER_LAZY_VAL)) |
| 54 | + unsafe.compareAndSwapLong(t, offset, e, n) |
| 55 | + } |
| 56 | + |
| 57 | + def setFlag(t: Object, offset: Long, v: Int, ord: Int): Unit = { |
| 58 | + if (debug) |
| 59 | + println(s"setFlag($t, $offset, $v, $ord)") |
| 60 | + var retry = true |
| 61 | + while (retry) { |
| 62 | + val cur = get(t, offset) |
| 63 | + if (STATE(cur, ord) == 1) retry = !CAS(t, offset, cur, v, ord) |
| 64 | + else { |
| 65 | + // cur == 2, somebody is waiting on monitor |
| 66 | + if (CAS(t, offset, cur, v, ord)) { |
| 67 | + val monitor = getMonitor(t, ord) |
| 68 | + monitor.synchronized { |
| 69 | + monitor.notifyAll() |
| 70 | + } |
| 71 | + retry = false |
| 72 | + } |
| 73 | + } |
| 74 | + } |
| 75 | + } |
| 76 | + |
| 77 | + def wait4Notification(t: Object, offset: Long, cur: Long, ord: Int): Unit = { |
| 78 | + if (debug) |
| 79 | + println(s"wait4Notification($t, $offset, $cur, $ord)") |
| 80 | + var retry = true |
| 81 | + while (retry) { |
| 82 | + val cur = get(t, offset) |
| 83 | + val state = STATE(cur, ord) |
| 84 | + if (state == 1) CAS(t, offset, cur, 2, ord) |
| 85 | + else if (state == 2) { |
| 86 | + val monitor = getMonitor(t, ord) |
| 87 | + monitor.synchronized { |
| 88 | + if (STATE(get(t, offset), ord) == 2) // make sure notification did not happen yet. |
| 89 | + monitor.wait() |
| 90 | + } |
| 91 | + } |
| 92 | + else retry = false |
| 93 | + } |
| 94 | + } |
| 95 | + |
| 96 | + def get(t: Object, off: Long): Long = { |
| 97 | + if (debug) |
| 98 | + println(s"get($t, $off)") |
| 99 | + unsafe.getLongVolatile(t, off) |
| 100 | + } |
| 101 | + |
| 102 | + def getOffset(clz: Class[_], name: String): Long = { |
| 103 | + val r = unsafe.objectFieldOffset(clz.getDeclaredField(name)) |
| 104 | + if (debug) |
| 105 | + println(s"getOffset($clz, $name) = $r") |
| 106 | + r |
| 107 | + } |
| 108 | + |
| 109 | + object Names { |
| 110 | + final val state = "STATE" |
| 111 | + final val cas = "CAS" |
| 112 | + final val setFlag = "setFlag" |
| 113 | + final val wait4Notification = "wait4Notification" |
| 114 | + final val get = "get" |
| 115 | + final val getOffset = "getOffset" |
| 116 | + } |
| 117 | +} |
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