Squash: Fix bugs

trunk/3rdparty/gperftools-2-fit/src/sampler.h

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+// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
+// Copyright (c) 2008, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// ---
+// All Rights Reserved.
+//
+// Author: Daniel Ford
+
+#ifndef TCMALLOC_SAMPLER_H_
+#define TCMALLOC_SAMPLER_H_
+
+#include "config.h"
+#include <stddef.h>                     // for size_t
+#ifdef HAVE_STDINT_H
+#include <stdint.h>                     // for uint64_t, uint32_t, int32_t
+#endif
+#include <string.h>                     // for memcpy
+#include "base/basictypes.h"  // for ASSERT
+#include "internal_logging.h"  // for ASSERT
+#include "static_vars.h"
+
+namespace tcmalloc {
+
+//-------------------------------------------------------------------
+// Sampler to decide when to create a sample trace for an allocation
+// Not thread safe: Each thread should have it's own sampler object.
+// Caller must use external synchronization if used
+// from multiple threads.
+//
+// With 512K average sample step (the default):
+//  the probability of sampling a 4K allocation is about 0.00778
+//  the probability of sampling a 1MB allocation is about 0.865
+//  the probability of sampling a 1GB allocation is about 1.00000
+// In general, the probablity of sampling is an allocation of size X
+// given a flag value of Y (default 1M) is:
+//  1 - e^(-X/Y)
+//
+// With 128K average sample step:
+//  the probability of sampling a 1MB allocation is about 0.99966
+//  the probability of sampling a 1GB allocation is about 1.0
+//  (about 1 - 2**(-26))
+// With 1M average sample step:
+//  the probability of sampling a 4K allocation is about 0.00390
+//  the probability of sampling a 1MB allocation is about 0.632
+//  the probability of sampling a 1GB allocation is about 1.0
+//
+// The sampler works by representing memory as a long stream from
+// which allocations are taken. Some of the bytes in this stream are
+// marked and if an allocation includes a marked byte then it is
+// sampled. Bytes are marked according to a Poisson point process
+// with each byte being marked independently with probability
+// p = 1/tcmalloc_sample_parameter.  This makes the probability
+// of sampling an allocation of X bytes equal to the CDF of
+// a geometric with mean tcmalloc_sample_parameter. (ie. the
+// probability that at least one byte in the range is marked). This
+// is accurately given by the CDF of the corresponding exponential
+// distribution : 1 - e^(-X/tcmalloc_sample_parameter_)
+// Independence of the byte marking ensures independence of
+// the sampling of each allocation.
+//
+// This scheme is implemented by noting that, starting from any
+// fixed place, the number of bytes until the next marked byte
+// is geometrically distributed. This number is recorded as
+// bytes_until_sample_.  Every allocation subtracts from this
+// number until it is less than 0. When this happens the current
+// allocation is sampled.
+//
+// When an allocation occurs, bytes_until_sample_ is reset to
+// a new independtly sampled geometric number of bytes. The
+// memoryless property of the point process means that this may
+// be taken as the number of bytes after the end of the current
+// allocation until the next marked byte. This ensures that
+// very large allocations which would intersect many marked bytes
+// only result in a single call to PickNextSamplingPoint.
+//-------------------------------------------------------------------
+
+class SamplerTest;
+
+class PERFTOOLS_DLL_DECL Sampler {
+ public:
+  constexpr Sampler() {}
+
+  // Initialize this sampler.
+  void Init(uint64_t seed);
+
+  // Record allocation of "k" bytes.  Return true if no further work
+  // is need, and false if allocation needed to be sampled.
+  bool RecordAllocation(size_t k);
+
+  // Same as above (but faster), except:
+  // a) REQUIRES(k < std::numeric_limits<ssize_t>::max())
+  // b) if this returns false, you must call RecordAllocation
+  //    to confirm if sampling truly needed.
+  //
+  // The point of this function is to only deal with common case of no
+  // sampling and let caller (which is in malloc fast-path) to
+  // "escalate" to fuller and slower logic only if necessary.
+  bool TryRecordAllocationFast(size_t k);
+
+  // Generate a geometric with mean 512K (or FLAG_tcmalloc_sample_parameter)
+  ssize_t PickNextSamplingPoint();
+
+  // Returns the current sample period
+  static int GetSamplePeriod();
+
+  // The following are public for the purposes of testing
+  static uint64_t NextRandom(uint64_t rnd_);  // Returns the next prng value
+
+  // C++03 requires that types stored in TLS be POD.  As a result, you must
+  // initialize these members to {0, 0, false} before using this class!
+  //
+  // TODO(ahh): C++11 support will let us make these private.
+
+  // Bytes until we sample next.
+  //
+  // More specifically when bytes_until_sample_ is X, we can allocate
+  // X bytes without triggering sampling; on the (X+1)th allocated
+  // byte, the containing allocation will be sampled.
+  //
+  // Always non-negative with only very brief exceptions (see
+  // DecrementFast{,Finish}, so casting to size_t is ok.
+ private:
+  friend class SamplerTest;
+  bool RecordAllocationSlow(size_t k);
+
+  ssize_t bytes_until_sample_{};
+  uint64_t rnd_{};  // Cheap random number generator
+  bool initialized_{};
+};
+
+inline bool Sampler::RecordAllocation(size_t k) {
+  // The first time we enter this function we expect bytes_until_sample_
+  // to be zero, and we must call SampleAllocationSlow() to ensure
+  // proper initialization of static vars.
+  ASSERT(Static::IsInited() || bytes_until_sample_ == 0);
+
+  // Note that we have to deal with arbitrarily large values of k
+  // here. Thus we're upcasting bytes_until_sample_ to unsigned rather
+  // than the other way around. And this is why this code cannot be
+  // merged with DecrementFast code below.
+  if (static_cast<size_t>(bytes_until_sample_) < k) {
+    bool result = RecordAllocationSlow(k);
+    ASSERT(Static::IsInited());
+    return result;
+  } else {
+    bytes_until_sample_ -= k;
+    ASSERT(Static::IsInited());
+    return true;
+  }
+}
+
+inline bool Sampler::TryRecordAllocationFast(size_t k) {
+  // For efficiency reason, we're testing bytes_until_sample_ after
+  // decrementing it by k. This allows compiler to do sub <reg>, <mem>
+  // followed by conditional jump on sign. But it is correct only if k
+  // is actually smaller than largest ssize_t value. Otherwise
+  // converting k to signed value overflows.
+  //
+  // It would be great for generated code to be sub <reg>, <mem>
+  // followed by conditional jump on 'carry', which would work for
+  // arbitrary values of k, but there seem to be no way to express
+  // that in C++.
+  //
+  // Our API contract explicitly states that only small values of k
+  // are permitted. And thus it makes sense to assert on that.
+  ASSERT(static_cast<ssize_t>(k) >= 0);
+
+  bytes_until_sample_ -= static_cast<ssize_t>(k);
+  if (PREDICT_FALSE(bytes_until_sample_ < 0)) {
+    // Note, we undo sampling counter update, since we're not actually
+    // handling slow path in the "needs sampling" case (calling
+    // RecordAllocationSlow to reset counter). And we do that in order
+    // to avoid non-tail calls in malloc fast-path. See also comments
+    // on declaration inside Sampler class.
+    //
+    // volatile is used here to improve compiler's choice of
+    // instuctions. We know that this path is very rare and that there
+    // is no need to keep previous value of bytes_until_sample_ in
+    // register. This helps compiler generate slightly more efficient
+    // sub <reg>, <mem> instruction for subtraction above.
+    volatile ssize_t *ptr =
+        const_cast<volatile ssize_t *>(&bytes_until_sample_);
+    *ptr += k;
+    return false;
+  }
+  return true;
+}
+
+// Inline functions which are public for testing purposes
+
+// Returns the next prng value.
+// pRNG is: aX+b mod c with a = 0x5DEECE66D, b =  0xB, c = 1<<48
+// This is the lrand64 generator.
+inline uint64_t Sampler::NextRandom(uint64_t rnd) {
+  const uint64_t prng_mult = 0x5DEECE66DULL;
+  const uint64_t prng_add = 0xB;
+  const uint64_t prng_mod_power = 48;
+  const uint64_t prng_mod_mask =
+      ~((~static_cast<uint64_t>(0)) << prng_mod_power);
+  return (prng_mult * rnd + prng_add) & prng_mod_mask;
+}
+
+}  // namespace tcmalloc
+
+#endif  // TCMALLOC_SAMPLER_H_