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// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package pprof
import "unsafe"
// A profMap is a map from (stack, tag) to mapEntry.
// It grows without bound, but that's assumed to be OK.
type profMap struct {
hash map[uintptr]*profMapEntry
all *profMapEntry
last *profMapEntry
free []profMapEntry
freeStk []uintptr
}
// A profMapEntry is a single entry in the profMap.
type profMapEntry struct {
nextHash *profMapEntry // next in hash list
nextAll *profMapEntry // next in list of all entries
stk []uintptr
tag unsafe.Pointer
count int64
}
func (m *profMap) lookup(stk []uint64, tag unsafe.Pointer) *profMapEntry {
// Compute hash of (stk, tag).
h := uintptr(0)
for _, x := range stk {
h = h<<8 | (h >> (8 * (unsafe.Sizeof(h) - 1)))
h += uintptr(x) * 41
}
h = h<<8 | (h >> (8 * (unsafe.Sizeof(h) - 1)))
h += uintptr(tag) * 41
// Find entry if present.
var last *profMapEntry
Search:
for e := m.hash[h]; e != nil; last, e = e, e.nextHash {
if len(e.stk) != len(stk) || e.tag != tag {
continue
}
for j := range stk {
if e.stk[j] != uintptr(stk[j]) {
continue Search
}
}
// Move to front.
if last != nil {
last.nextHash = e.nextHash
e.nextHash = m.hash[h]
m.hash[h] = e
}
return e
}
// Add new entry.
if len(m.free) < 1 {
m.free = make([]profMapEntry, 128)
}
e := &m.free[0]
m.free = m.free[1:]
e.nextHash = m.hash[h]
e.tag = tag
if len(m.freeStk) < len(stk) {
m.freeStk = make([]uintptr, 1024)
}
// Limit cap to prevent append from clobbering freeStk.
e.stk = m.freeStk[:len(stk):len(stk)]
m.freeStk = m.freeStk[len(stk):]
for j := range stk {
e.stk[j] = uintptr(stk[j])
}
if m.hash == nil {
m.hash = make(map[uintptr]*profMapEntry)
}
m.hash[h] = e
if m.all == nil {
m.all = e
m.last = e
} else {
m.last.nextAll = e
m.last = e
}
return e
}
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