Quelle CodeAddressService.h Sprache: C

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef CodeAddressService_h__
#define CodeAddressService_h__

#include <cstddef>
#include <cstdint>
#include <cstring>
#include "mozilla/AllocPolicy.h"
#include "mozilla/Assertions.h"
#include "mozilla/HashFunctions.h"
#include "mozilla/HashTable.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/StackWalk.h"

namespace mozilla {

namespace detail {

template <class AllocPolicy>
class CodeAddressServiceAllocPolicy : public AllocPolicy {
public:
  char* strdup_(const char* aStr) {
    char* s = AllocPolicy::template pod_malloc<char>(strlen(aStr) + 1);
    if (!s) {
      MOZ_CRASH("CodeAddressService OOM");
    }
    strcpy(s, aStr);
    return s;
  }
};

// Default implementation of DescribeCodeAddressLock.
struct DefaultDescribeCodeAddressLock {
  static void Unlock() {}
  static void Lock() {}
  // Because CodeAddressService asserts that IsLocked() is true, returning true
  // here is a sensible default when there is no relevant lock.
  static bool IsLocked() { return true; }
};

}  // namespace detail

// This class is used to print details about code locations.
//
// |AllocPolicy_| must adhere to the description in mfbt/AllocPolicy.h.
//
// |DescribeCodeAddressLock| is needed when the callers may be holding a lock
// used by MozDescribeCodeAddress.  |DescribeCodeAddressLock| must implement
// static methods IsLocked(), Unlock() and Lock().
template <class AllocPolicy_ = MallocAllocPolicy,
          class DescribeCodeAddressLock =
              detail::DefaultDescribeCodeAddressLock>
class CodeAddressService
    : private detail::CodeAddressServiceAllocPolicy<AllocPolicy_> {
protected:
  // GetLocation() is the key function in this class.  It's basically a wrapper
  // around MozDescribeCodeAddress.
  //
  // However, MozDescribeCodeAddress is very slow on some platforms, and we
  // have lots of repeated (i.e. same PC) calls to it.  So we do some caching
  // of results.  Each cached result includes two strings (|mFunction| and
  // |mLibrary|), so we also optimize them for space in the following ways.
  //
  // - The number of distinct library names is small, e.g. a few dozen.  There
  //   is lots of repetition, especially of libxul.  So we intern them in their
  //   own table, which saves space over duplicating them for each cache entry.
  //
  // - The number of distinct function names is much higher, so we duplicate
  //   them in each cache entry.  That's more space-efficient than interning
  //   because entries containing single-occurrence function names are quickly
  //   overwritten, and their copies released.  In addition, empty function
  //   names are common, so we use nullptr to represent them compactly.

  using AllocPolicy = detail::CodeAddressServiceAllocPolicy<AllocPolicy_>;
  using StringHashSet = HashSet<const char*, CStringHasher, AllocPolicy>;

  StringHashSet mLibraryStrings;

  struct Entry : private AllocPolicy {
    const void* mPc;
    char* mFunction;       // owned by the Entry;  may be null
    const char* mLibrary;  // owned by mLibraryStrings;  never null
                           //   in a non-empty entry is in use
    ptrdiff_t mLOffset;
    char* mFileName;  // owned by the Entry; may be null
    uint32_t mLineNo : 31;
    uint32_t mInUse : 1;  // is the entry used?

    Entry()
        : mPc(0),
          mFunction(nullptr),
          mLibrary(nullptr),
          mLOffset(0),
          mFileName(nullptr),
          mLineNo(0),
          mInUse(0) {}

    ~Entry() {
      // We don't free mLibrary because it's externally owned.
      AllocPolicy::free_(mFunction);
      AllocPolicy::free_(mFileName);
    }

    void Replace(const void* aPc, const char* aFunction, const char* aLibrary,
                 ptrdiff_t aLOffset, const char* aFileName,
                 unsigned long aLineNo) {
      mPc = aPc;

      // Convert "" to nullptr.  Otherwise, make a copy of the name.
      AllocPolicy::free_(mFunction);
      mFunction = !aFunction[0] ? nullptr : AllocPolicy::strdup_(aFunction);
      AllocPolicy::free_(mFileName);
      mFileName = !aFileName[0] ? nullptr : AllocPolicy::strdup_(aFileName);

      mLibrary = aLibrary;
      mLOffset = aLOffset;
      mLineNo = aLineNo;

      mInUse = 1;
    }

    size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const {
      // Don't measure mLibrary because it's externally owned.
      size_t n = 0;
      n += aMallocSizeOf(mFunction);
      n += aMallocSizeOf(mFileName);
      return n;
    }
  };

  const char* InternLibraryString(const char* aString) {
    auto p = mLibraryStrings.lookupForAdd(aString);
    if (p) {
      return *p;
    }

    const char* newString = AllocPolicy::strdup_(aString);
    if (!mLibraryStrings.add(p, newString)) {
      MOZ_CRASH("CodeAddressService OOM");
    }
    return newString;
  }

  Entry& GetEntry(const void* aPc) {
    MOZ_ASSERT(DescribeCodeAddressLock::IsLocked());

    uint32_t index = HashGeneric(aPc) & kMask;
    MOZ_ASSERT(index < kNumEntries);
    Entry& entry = mEntries[index];

    if (!entry.mInUse || entry.mPc != aPc) {
      mNumCacheMisses++;

      // MozDescribeCodeAddress can (on Linux) acquire a lock inside
      // the shared library loader.  Another thread might call malloc
      // while holding that lock (when loading a shared library).  So
      // we have to exit the lock around this call.  For details, see
      // https://bugzilla.mozilla.org/show_bug.cgi?id=363334#c3
      MozCodeAddressDetails details;
      {
        DescribeCodeAddressLock::Unlock();
        (void)MozDescribeCodeAddress(const_cast<void*>(aPc), &details);
        DescribeCodeAddressLock::Lock();
      }

      const char* library = InternLibraryString(details.library);
      entry.Replace(aPc, details.function, library, details.loffset,
                    details.filename, details.lineno);

    } else {
      mNumCacheHits++;
    }

    MOZ_ASSERT(entry.mPc == aPc);

    return entry;
  }

  // A direct-mapped cache.  When doing dmd::Analyze() just after starting
  // desktop Firefox (which is similar to analyzing after a longer-running
  // session, thanks to the limit on how many records we print), a cache with
  // 2^24 entries (which approximates an infinite-entry cache) has a ~91% hit
  // rate.  A cache with 2^12 entries has a ~83% hit rate, and takes up ~85 KiB
  // (on 32-bit platforms) or ~150 KiB (on 64-bit platforms).
  static const size_t kNumEntries = 1 << 12;
  static const size_t kMask = kNumEntries - 1;
  Entry mEntries[kNumEntries];

  size_t mNumCacheHits;
  size_t mNumCacheMisses;

public:
  CodeAddressService()
      : mLibraryStrings(64), mEntries(), mNumCacheHits(0), mNumCacheMisses(0) {}

  ~CodeAddressService() {
    for (auto iter = mLibraryStrings.iter(); !iter.done(); iter.next()) {
      AllocPolicy::free_(const_cast<char*>(iter.get()));
    }
  }

  // Returns the minimum number of characters necessary to format the frame
  // information, without the terminating null. The buffer will be truncated
  // if the returned value is greater than aBufLen-1.
  int GetLocation(uint32_t aFrameNumber, const void* aPc, char* aBuf,
                  size_t aBufLen) {
    Entry& entry = GetEntry(aPc);
    return MozFormatCodeAddress(aBuf, aBufLen, aFrameNumber, entry.mPc,
                                entry.mFunction, entry.mLibrary, entry.mLOffset,
                                entry.mFileName, entry.mLineNo);
  }

  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const {
    size_t n = aMallocSizeOf(this);
    for (uint32_t i = 0; i < kNumEntries; i++) {
      n += mEntries[i].SizeOfExcludingThis(aMallocSizeOf);
    }

    n += mLibraryStrings.shallowSizeOfExcludingThis(aMallocSizeOf);
    for (auto iter = mLibraryStrings.iter(); !iter.done(); iter.next()) {
      n += aMallocSizeOf(iter.get());
    }

    return n;
  }

  size_t CacheCapacity() const { return kNumEntries; }

  size_t CacheCount() const {
    size_t n = 0;
    for (size_t i = 0; i < kNumEntries; i++) {
      if (mEntries[i].mInUse) {
        n++;
      }
    }
    return n;
  }

  size_t NumCacheHits() const { return mNumCacheHits; }
  size_t NumCacheMisses() const { return mNumCacheMisses; }
};

}  // namespace mozilla

#endif  // CodeAddressService_h__

quality93%

¤ Dauer der Verarbeitung: 0.1 Sekunden (vorverarbeitet) ¤

Wurzel

Suchen

Beweissystem der NASA

Beweissystem Isabelle

NIST Cobol Testsuite

Cephes Mathematical Library

Wiener Entwicklungsmethode

Haftungshinweis

Die Informationen auf dieser Webseite wurden nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit, noch Qualität der bereit gestellten Informationen zugesichert.

Bemerkung:

Die farbliche Syntaxdarstellung ist noch experimentell.