gecko-dev/xpcom/base/nsMemoryInfoDumper.cpp

/* -*- 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/. */

#include "mozilla/nsMemoryInfoDumper.h"
#include "nsDumpUtils.h"

#include "mozilla/unused.h"
#include "mozilla/dom/ContentParent.h"
#include "mozilla/dom/ContentChild.h"
#include "nsIConsoleService.h"
#include "nsICycleCollectorListener.h"
#include "nsIMemoryReporter.h"
#include "nsDirectoryServiceDefs.h"
#include "nsGZFileWriter.h"
#include "nsJSEnvironment.h"
#include "nsPrintfCString.h"
#include "nsISimpleEnumerator.h"
#include "nsServiceManagerUtils.h"
#include "nsIFile.h"

#ifdef XP_WIN
#include <process.h>
#define getpid _getpid
#else
#include <unistd.h>
#endif

#if defined(XP_LINUX) || defined(__FreeBSD__)
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#endif

using namespace mozilla;
using namespace mozilla::dom;

namespace {

class DumpMemoryInfoToTempDirRunnable : public nsRunnable
{
public:
  DumpMemoryInfoToTempDirRunnable(const nsAString& aIdentifier,
                                  bool aMinimizeMemoryUsage)
      : mIdentifier(aIdentifier)
      , mMinimizeMemoryUsage(aMinimizeMemoryUsage)
  {}

  NS_IMETHOD Run()
  {
    nsCOMPtr<nsIMemoryInfoDumper> dumper = do_GetService("@mozilla.org/memory-info-dumper;1");
    dumper->DumpMemoryInfoToTempDir(mIdentifier, mMinimizeMemoryUsage);
    return NS_OK;
  }

private:
  const nsString mIdentifier;
  const bool mMinimizeMemoryUsage;
};

class GCAndCCLogDumpRunnable : public nsRunnable
{
public:
  GCAndCCLogDumpRunnable(const nsAString& aIdentifier,
                         bool aDumpAllTraces,
                         bool aDumpChildProcesses)
    : mIdentifier(aIdentifier)
    , mDumpAllTraces(aDumpAllTraces)
    , mDumpChildProcesses(aDumpChildProcesses)
  {}

  NS_IMETHOD Run()
  {
    nsCOMPtr<nsIMemoryInfoDumper> dumper =
      do_GetService("@mozilla.org/memory-info-dumper;1");

    nsString ccLogPath, gcLogPath;
    dumper->DumpGCAndCCLogsToFile(mIdentifier, mDumpAllTraces,
                                  mDumpChildProcesses, gcLogPath, ccLogPath);
    return NS_OK;
  }

private:
  const nsString mIdentifier;
  const bool mDumpAllTraces;
  const bool mDumpChildProcesses;
};

} // anonymous namespace

#if defined(XP_LINUX) || defined(__FreeBSD__) // {
namespace {

/*
 * The following code supports dumping about:memory upon receiving a signal.
 *
 * We listen for the following signals:
 *
 *  - SIGRTMIN:     Dump our memory reporters (and those of our child
 *                  processes),
 *  - SIGRTMIN + 1: Dump our memory reporters (and those of our child
 *                  processes) after minimizing memory usage, and
 *  - SIGRTMIN + 2: Dump the GC and CC logs in this and our child processes.
 *
 * When we receive one of these signals, we write the signal number to a pipe.
 * The IO thread then notices that the pipe has been written to, and kicks off
 * the appropriate task on the main thread.
 *
 * This scheme is similar to using signalfd(), except it's portable and it
 * doesn't require the use of sigprocmask, which is problematic because it
 * masks signals received by child processes.
 *
 * In theory, we could use Chromium's MessageLoopForIO::CatchSignal() for this.
 * But that uses libevent, which does not handle the realtime signals (bug
 * 794074).
 */

// It turns out that at least on some systems, SIGRTMIN is not a compile-time
// constant, so these have to be set at runtime.
static uint8_t sDumpAboutMemorySignum;         // SIGRTMIN
static uint8_t sDumpAboutMemoryAfterMMUSignum; // SIGRTMIN + 1
static uint8_t sGCAndCCDumpSignum;             // SIGRTMIN + 2

void doMemoryReport(const nsCString& inputStr)
{
  bool doMMUMemoryReport = inputStr == NS_LITERAL_CSTRING("minimize memory report");
  LOG("FifoWatcher(command:%s) dispatching memory report runnable.", inputStr.get());
  nsRefPtr<DumpMemoryInfoToTempDirRunnable> runnable =
    new DumpMemoryInfoToTempDirRunnable(/* identifier = */ EmptyString(),
                                        doMMUMemoryReport);
  NS_DispatchToMainThread(runnable);
}

void doMemoryReport(const uint8_t recvSig)
{
  // Dump our memory reports (but run this on the main thread!).
  bool doMMUFirst = recvSig == sDumpAboutMemoryAfterMMUSignum;
  LOG("SignalWatcher(sig %d) dispatching memory report runnable.", recvSig);
  nsRefPtr<DumpMemoryInfoToTempDirRunnable> runnable =
    new DumpMemoryInfoToTempDirRunnable(/* identifier = */ EmptyString(),
                                        doMMUFirst);
  NS_DispatchToMainThread(runnable);
}

void doGCCCDump(const nsCString& inputStr)
{
  bool doAllTracesGCCCDump = inputStr == NS_LITERAL_CSTRING("gc log");
  LOG("FifoWatcher(command:%s) dispatching GC/CC log runnable.", inputStr.get());
  nsRefPtr<GCAndCCLogDumpRunnable> runnable =
    new GCAndCCLogDumpRunnable(/* identifier = */ EmptyString(),
                              doAllTracesGCCCDump,
                              /* dumpChildProcesses = */ true);
  NS_DispatchToMainThread(runnable);
}

void doGCCCDump(const uint8_t recvSig)
{
  LOG("SignalWatcher(sig %d) dispatching GC/CC log runnable.", recvSig);
  // Dump GC and CC logs (from the main thread).
  nsRefPtr<GCAndCCLogDumpRunnable> runnable =
    new GCAndCCLogDumpRunnable(
        /* identifier = */ EmptyString(),
        /* allTraces = */ true,
        /* dumpChildProcesses = */ true);
  NS_DispatchToMainThread(runnable);
}

} // anonymous namespace
#endif // XP_LINUX }

NS_IMPL_ISUPPORTS1(nsMemoryInfoDumper, nsIMemoryInfoDumper)

nsMemoryInfoDumper::nsMemoryInfoDumper()
{
}

nsMemoryInfoDumper::~nsMemoryInfoDumper()
{
}

/* static */ void
nsMemoryInfoDumper::Initialize()
{
#if defined(XP_LINUX) || defined(__FreeBSD__)
  SignalPipeWatcher* sw = SignalPipeWatcher::GetSingleton();

  // Dump memory reporters (and those of our child processes)
  sDumpAboutMemorySignum = SIGRTMIN;
  sw->RegisterCallback(sDumpAboutMemorySignum, doMemoryReport);
  // Dump our memory reporters after minimizing memory usage
  sDumpAboutMemoryAfterMMUSignum = SIGRTMIN + 1;
  sw->RegisterCallback(sDumpAboutMemoryAfterMMUSignum, doMemoryReport);
  // Dump the GC and CC logs in this and our child processes.
  sGCAndCCDumpSignum = SIGRTMIN + 2;
  sw->RegisterCallback(sGCAndCCDumpSignum, doGCCCDump);

  if (FifoWatcher::MaybeCreate()) {
    FifoWatcher* fw = FifoWatcher::GetSingleton();
    // Dump our memory reports (but run this on the main thread!).
    fw->RegisterCallback(NS_LITERAL_CSTRING("memory report"),
                         doMemoryReport);
    fw->RegisterCallback(NS_LITERAL_CSTRING("minimize memory report"),
                         doMemoryReport);
    // Dump GC and CC logs (from the main thread).
    fw->RegisterCallback(NS_LITERAL_CSTRING("gc log"),
                         doGCCCDump);
    fw->RegisterCallback(NS_LITERAL_CSTRING("abbreviated gc log"),
                         doGCCCDump);
  }
#endif
}

static void
EnsureNonEmptyIdentifier(nsAString& aIdentifier)
{
  if (!aIdentifier.IsEmpty()) {
    return;
  }

  // If the identifier is empty, set it to the number of whole seconds since the
  // epoch.  This identifier will appear in the files that this process
  // generates and also the files generated by this process's children, allowing
  // us to identify which files are from the same memory report request.
  aIdentifier.AppendInt(static_cast<int64_t>(PR_Now()) / 1000000);
}

NS_IMETHODIMP
nsMemoryInfoDumper::DumpGCAndCCLogsToFile(const nsAString& aIdentifier,
                                          bool aDumpAllTraces,
                                          bool aDumpChildProcesses,
                                          nsAString& aGCLogPath,
                                          nsAString& aCCLogPath)
{
  nsString identifier(aIdentifier);
  EnsureNonEmptyIdentifier(identifier);

  if (aDumpChildProcesses) {
    nsTArray<ContentParent*> children;
    ContentParent::GetAll(children);
    for (uint32_t i = 0; i < children.Length(); i++) {
      unused << children[i]->SendDumpGCAndCCLogsToFile(
        identifier, aDumpAllTraces, aDumpChildProcesses);
    }
  }

  nsCOMPtr<nsICycleCollectorListener> logger =
    do_CreateInstance("@mozilla.org/cycle-collector-logger;1");
  logger->SetFilenameIdentifier(identifier);

  if (aDumpAllTraces) {
    nsCOMPtr<nsICycleCollectorListener> allTracesLogger;
    logger->AllTraces(getter_AddRefs(allTracesLogger));
    logger = allTracesLogger;
  }

  nsJSContext::CycleCollectNow(logger);

  logger->GetGcLogPath(aGCLogPath);
  logger->GetCcLogPath(aCCLogPath);

  return NS_OK;
}

namespace mozilla {

#define DUMP(o, s) \
  do { \
    nsresult rv = (o)->Write(s); \
    if (NS_WARN_IF(NS_FAILED(rv))) \
      return rv; \
  } while (0)

class DumpReportCallback MOZ_FINAL : public nsIHandleReportCallback
{
public:
  NS_DECL_ISUPPORTS

  DumpReportCallback(nsGZFileWriter* aWriter)
    : mIsFirst(true)
    , mWriter(aWriter)
  {}

  NS_IMETHOD Callback(const nsACString &aProcess, const nsACString &aPath,
      int32_t aKind, int32_t aUnits, int64_t aAmount,
      const nsACString &aDescription,
      nsISupports *aData)
  {
    if (mIsFirst) {
      DUMP(mWriter, "[");
      mIsFirst = false;
    } else {
      DUMP(mWriter, ",");
    }

    nsAutoCString process;
    if (aProcess.IsEmpty()) {
      // If the process is empty, the report originated with the process doing
      // the dumping.  In that case, generate the process identifier, which is of
      // the form "$PROCESS_NAME (pid $PID)", or just "(pid $PID)" if we don't
      // have a process name.  If we're the main process, we let $PROCESS_NAME be
      // "Main Process".
      if (XRE_GetProcessType() == GeckoProcessType_Default) {
        // We're the main process.
        process.AssignLiteral("Main Process");
      } else if (ContentChild *cc = ContentChild::GetSingleton()) {
        // Try to get the process name from ContentChild.
        cc->GetProcessName(process);
      }
      ContentChild::AppendProcessId(process);

    } else {
      // Otherwise, the report originated with another process and already has a
      // process name.  Just use that.
      process = aProcess;
    }

    DUMP(mWriter, "\n    {\"process\": \"");
    DUMP(mWriter, process);

    DUMP(mWriter, "\", \"path\": \"");
    nsCString path(aPath);
    path.ReplaceSubstring("\\", "\\\\");    /* <backslash> --> \\ */
    path.ReplaceSubstring("\"", "\\\"");    // " --> \"
    DUMP(mWriter, path);

    DUMP(mWriter, "\", \"kind\": ");
    DUMP(mWriter, nsPrintfCString("%d", aKind));

    DUMP(mWriter, ", \"units\": ");
    DUMP(mWriter, nsPrintfCString("%d", aUnits));

    DUMP(mWriter, ", \"amount\": ");
    DUMP(mWriter, nsPrintfCString("%lld", aAmount));

    nsCString description(aDescription);
    description.ReplaceSubstring("\\", "\\\\");    /* <backslash> --> \\ */
    description.ReplaceSubstring("\"", "\\\"");    // " --> \"
    description.ReplaceSubstring("\n", "\\n");     // <newline> --> \n
    DUMP(mWriter, ", \"description\": \"");
    DUMP(mWriter, description);
    DUMP(mWriter, "\"}");

    return NS_OK;
  }

private:
  bool mIsFirst;
  nsRefPtr<nsGZFileWriter> mWriter;
};

NS_IMPL_ISUPPORTS1(DumpReportCallback, nsIHandleReportCallback)

} // namespace mozilla

static void
MakeFilename(const char *aPrefix, const nsAString &aIdentifier,
             const char *aSuffix, nsACString &aResult)
{
  aResult = nsPrintfCString("%s-%s-%d.%s",
                            aPrefix,
                            NS_ConvertUTF16toUTF8(aIdentifier).get(),
                            getpid(), aSuffix);
}

#ifdef MOZ_DMD
struct DMDWriteState
{
  static const size_t kBufSize = 4096;
  char mBuf[kBufSize];
  nsRefPtr<nsGZFileWriter> mGZWriter;

  DMDWriteState(nsGZFileWriter *aGZWriter)
    : mGZWriter(aGZWriter)
  {}
};

static void
DMDWrite(void* aState, const char* aFmt, va_list ap)
{
  DMDWriteState *state = (DMDWriteState*)aState;
  vsnprintf(state->mBuf, state->kBufSize, aFmt, ap);
  unused << state->mGZWriter->Write(state->mBuf);
}
#endif

static nsresult
DumpHeader(nsIGZFileWriter* aWriter)
{
  // Increment this number if the format changes.
  //
  // This is the first write to the file, and it causes |aWriter| to allocate
  // over 200 KiB of memory.
  //
  DUMP(aWriter, "{\n  \"version\": 1,\n");

  DUMP(aWriter, "  \"hasMozMallocUsableSize\": ");

  nsCOMPtr<nsIMemoryReporterManager> mgr =
    do_GetService("@mozilla.org/memory-reporter-manager;1");
  if (NS_WARN_IF(!mgr))
    return NS_ERROR_UNEXPECTED;

  DUMP(aWriter, mgr->GetHasMozMallocUsableSize() ? "true" : "false");
  DUMP(aWriter, ",\n");
  DUMP(aWriter, "  \"reports\": ");

  return NS_OK;
}

static nsresult
DumpFooter(nsIGZFileWriter* aWriter)
{
  DUMP(aWriter, "\n  ]\n}\n");

  return NS_OK;
}

class TempDirMemoryFinishCallback MOZ_FINAL : public nsIFinishReportingCallback
{
public:
  NS_DECL_ISUPPORTS

  TempDirMemoryFinishCallback(nsGZFileWriter *aWriter,
                              nsIFile *aTmpFile,
                              const nsCString &aFilename,
                              const nsString &aIdentifier)
    : mrWriter(aWriter)
    , mrTmpFile(aTmpFile)
    , mrFilename(aFilename)
    , mIdentifier(aIdentifier)
  {}

  NS_IMETHOD Callback(nsISupports *aData);

private:
  nsRefPtr<nsGZFileWriter> mrWriter;
  nsCOMPtr<nsIFile> mrTmpFile;
  nsCString mrFilename;
  nsString mIdentifier;
};

NS_IMPL_ISUPPORTS1(TempDirMemoryFinishCallback, nsIFinishReportingCallback)

NS_IMETHODIMP
nsMemoryInfoDumper::DumpMemoryInfoToTempDir(const nsAString& aIdentifier,
                                            bool aMinimizeMemoryUsage)
{
  nsString identifier(aIdentifier);
  EnsureNonEmptyIdentifier(identifier);

#ifdef MOZ_DMD
  // Clear DMD's reportedness state before running the memory reporters, to
  // avoid spurious twice-reported warnings.
  dmd::ClearReports();
#endif

  // Open a new file named something like
  //
  //   incomplete-memory-report-<identifier>-<pid>.json.gz
  //
  // in NS_OS_TEMP_DIR for writing.  When we're finished writing the report,
  // we'll rename this file and get rid of the "incomplete-" prefix.
  //
  // We do this because we don't want scripts which poll the filesystem
  // looking for memory report dumps to grab a file before we're finished
  // writing to it.

  // Note that |mrFilename| is missing the "incomplete-" prefix; we'll tack
  // that on in a moment.
  nsCString mrFilename;
  // The "unified" indicates that we merge the memory reports from all
  // processes and write out one file, rather than a separate file for
  // each process as was the case before bug 946407.  This is so that
  // the get_about_memory.py script in the B2G repository can
  // determine when it's done waiting for files to appear.
  MakeFilename("unified-memory-report", identifier, "json.gz", mrFilename);

  nsCOMPtr<nsIFile> mrTmpFile;
  nsresult rv;
  // In Android case, this function will open a file named aFilename under
  // specific folder (/data/local/tmp/memory-reports). Otherwise, it will
  // open a file named aFilename under "NS_OS_TEMP_DIR".
  rv = nsDumpUtils::OpenTempFile(NS_LITERAL_CSTRING("incomplete-") +
                                 mrFilename,
                                 getter_AddRefs(mrTmpFile),
                                 NS_LITERAL_CSTRING("memory-reports"));
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  nsRefPtr<nsGZFileWriter> mrWriter = new nsGZFileWriter();
  rv = mrWriter->Init(mrTmpFile);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  // Dump the memory reports to the file.
  rv = DumpHeader(mrWriter);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  // Process reporters.
  nsCOMPtr<nsIMemoryReporterManager> mgr =
    do_GetService("@mozilla.org/memory-reporter-manager;1");
  nsRefPtr<DumpReportCallback> dumpReport = new DumpReportCallback(mrWriter);
  nsRefPtr<nsIFinishReportingCallback> finishReport =
    new TempDirMemoryFinishCallback(mrWriter, mrTmpFile, mrFilename, identifier);
  rv = mgr->GetReportsExtended(dumpReport, nullptr,
                               finishReport, nullptr,
                               aMinimizeMemoryUsage,
                               identifier);
  return rv;
}

#ifdef MOZ_DMD
nsresult
nsMemoryInfoDumper::DumpDMD(const nsAString &aIdentifier)
{
  nsresult rv;

  // Create a filename like dmd-<identifier>-<pid>.txt.gz, which will be used
  // if DMD is enabled.
  nsCString dmdFilename;
  MakeFilename("dmd", aIdentifier, "txt.gz", dmdFilename);

  // Open a new DMD file named |dmdFilename| in NS_OS_TEMP_DIR for writing,
  // and dump DMD output to it.  This must occur after the memory reporters
  // have been run (above), but before the memory-reports file has been
  // renamed (so scripts can detect the DMD file, if present).

  nsCOMPtr<nsIFile> dmdFile;
  rv = nsDumpUtils::OpenTempFile(dmdFilename,
                                 getter_AddRefs(dmdFile),
                                 NS_LITERAL_CSTRING("memory-reports"));
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  nsRefPtr<nsGZFileWriter> dmdWriter = new nsGZFileWriter();
  rv = dmdWriter->Init(dmdFile);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  // Dump DMD output to the file.

  DMDWriteState state(dmdWriter);
  dmd::Writer w(DMDWrite, &state);
  dmd::Dump(w);

  rv = dmdWriter->Finish();
  NS_WARN_IF(NS_FAILED(rv));
  return rv;
}
#endif  // MOZ_DMD

NS_IMETHODIMP
TempDirMemoryFinishCallback::Callback(nsISupports *aData)
{
  nsresult rv;

  rv = DumpFooter(mrWriter);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  // The call to Finish() deallocates the memory allocated by mrWriter's first
  // DUMP() call (within DumpProcessMemoryReportsToGZFileWriter()).  Because
  // that memory was live while the memory reporters ran and thus measured by
  // them -- by "heap-allocated" if nothing else -- we want DMD to see it as
  // well.  So we deliberately don't call Finish() until after DMD finishes.
  rv = mrWriter->Finish();
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  // Rename the memory reports file, now that we're done writing all the files.
  // Its final name is "memory-report<-identifier>-<pid>.json.gz".

  nsCOMPtr<nsIFile> mrFinalFile;
  rv = NS_GetSpecialDirectory(NS_OS_TEMP_DIR, getter_AddRefs(mrFinalFile));
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

#ifdef ANDROID
  rv = mrFinalFile->AppendNative(NS_LITERAL_CSTRING("memory-reports"));
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;
#endif

  rv = mrFinalFile->AppendNative(mrFilename);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  rv = mrFinalFile->CreateUnique(nsIFile::NORMAL_FILE_TYPE, 0600);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  nsAutoString mrActualFinalFilename;
  rv = mrFinalFile->GetLeafName(mrActualFinalFilename);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  rv = mrTmpFile->MoveTo(/* directory */ nullptr, mrActualFinalFilename);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  // Write a message to the console.

  nsCOMPtr<nsIConsoleService> cs =
    do_GetService(NS_CONSOLESERVICE_CONTRACTID, &rv);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  nsString path;
  mrTmpFile->GetPath(path);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  nsString msg = NS_LITERAL_STRING(
    "nsIMemoryInfoDumper dumped reports to ");
  msg.Append(path);
  return cs->LogStringMessage(msg.get());
}

// This dumps the JSON footer and closes the file, and then calls the given
// nsIFinishDumpingCallback.
class FinishReportingCallback MOZ_FINAL : public nsIFinishReportingCallback
{
public:
  NS_DECL_ISUPPORTS

  FinishReportingCallback(nsIFinishDumpingCallback* aFinishDumping,
                          nsISupports* aFinishDumpingData)
    : mFinishDumping(aFinishDumping)
    , mFinishDumpingData(aFinishDumpingData)
  {}

  NS_IMETHOD Callback(nsISupports* aData)
  {
    nsCOMPtr<nsIGZFileWriter> writer = do_QueryInterface(aData);
    NS_ENSURE_TRUE(writer, NS_ERROR_FAILURE);

    nsresult rv = DumpFooter(writer);
    NS_ENSURE_SUCCESS(rv, rv);

    rv = writer->Finish();
    NS_ENSURE_SUCCESS(rv, rv);

    if (!mFinishDumping) {
      return NS_OK;
    }

    return mFinishDumping->Callback(mFinishDumpingData);
  }

private:
  nsCOMPtr<nsIFinishDumpingCallback> mFinishDumping;
  nsCOMPtr<nsISupports> mFinishDumpingData;
};

NS_IMPL_ISUPPORTS1(FinishReportingCallback, nsIFinishReportingCallback)

NS_IMETHODIMP
nsMemoryInfoDumper::DumpMemoryReportsToNamedFile(
  const nsAString& aFilename,
  nsIFinishDumpingCallback* aFinishDumping,
  nsISupports* aFinishDumpingData)
{
  MOZ_ASSERT(!aFilename.IsEmpty());

  // Create the file.

  nsCOMPtr<nsIFile> mrFile;
  nsresult rv = NS_NewLocalFile(aFilename, false, getter_AddRefs(mrFile));
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  mrFile->InitWithPath(aFilename);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  bool exists;
  rv = mrFile->Exists(&exists);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  if (!exists) {
    rv = mrFile->Create(nsIFile::NORMAL_FILE_TYPE, 0644);
    if (NS_WARN_IF(NS_FAILED(rv)))
      return rv;
  }

  // Write the memory reports to the file.

  nsRefPtr<nsGZFileWriter> mrWriter = new nsGZFileWriter();
  rv = mrWriter->Init(mrFile);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  rv = DumpHeader(mrWriter);
  if (NS_WARN_IF(NS_FAILED(rv)))
    return rv;

  // Process reports and finish up.
  nsRefPtr<DumpReportCallback> dumpReport = new DumpReportCallback(mrWriter);
  nsRefPtr<FinishReportingCallback> finishReporting =
    new FinishReportingCallback(aFinishDumping, aFinishDumpingData);
  nsCOMPtr<nsIMemoryReporterManager> mgr =
    do_GetService("@mozilla.org/memory-reporter-manager;1");
  return mgr->GetReports(dumpReport, nullptr, finishReporting, mrWriter);
}

#undef DUMP