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106 lines
2.1 KiB
106 lines
2.1 KiB
package amqp
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import (
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"bytes"
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"fmt"
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"math/big"
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)
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const (
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free = 0
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allocated = 1
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)
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// allocator maintains a bitset of allocated numbers.
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type allocator struct {
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pool *big.Int
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last int
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low int
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high int
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}
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// NewAllocator reserves and frees integers out of a range between low and
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// high.
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//
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// O(N) worst case space used, where N is maximum allocated, divided by
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// sizeof(big.Word)
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func newAllocator(low, high int) *allocator {
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return &allocator{
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pool: big.NewInt(0),
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last: low,
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low: low,
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high: high,
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}
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}
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// String returns a string describing the contents of the allocator like
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// "allocator[low..high] reserved..until"
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//
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// O(N) where N is high-low
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func (a allocator) String() string {
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b := &bytes.Buffer{}
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fmt.Fprintf(b, "allocator[%d..%d]", a.low, a.high)
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for low := a.low; low <= a.high; low++ {
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high := low
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for a.reserved(high) && high <= a.high {
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high++
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}
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if high > low+1 {
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fmt.Fprintf(b, " %d..%d", low, high-1)
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} else if high > low {
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fmt.Fprintf(b, " %d", high-1)
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}
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low = high
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}
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return b.String()
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}
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// Next reserves and returns the next available number out of the range between
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// low and high. If no number is available, false is returned.
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//
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// O(N) worst case runtime where N is allocated, but usually O(1) due to a
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// rolling index into the oldest allocation.
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func (a *allocator) next() (int, bool) {
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wrapped := a.last
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// Find trailing bit
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for ; a.last <= a.high; a.last++ {
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if a.reserve(a.last) {
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return a.last, true
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}
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}
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// Find preceeding free'd pool
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a.last = a.low
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for ; a.last < wrapped; a.last++ {
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if a.reserve(a.last) {
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return a.last, true
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}
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}
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return 0, false
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}
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// reserve claims the bit if it is not already claimed, returning true if
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// succesfully claimed.
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func (a *allocator) reserve(n int) bool {
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if a.reserved(n) {
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return false
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}
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a.pool.SetBit(a.pool, n-a.low, allocated)
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return true
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}
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// reserved returns true if the integer has been allocated
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func (a *allocator) reserved(n int) bool {
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return a.pool.Bit(n-a.low) == allocated
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}
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// release frees the use of the number for another allocation
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func (a *allocator) release(n int) {
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a.pool.SetBit(a.pool, n-a.low, free)
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}
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