xpcom/base/AvailableMemoryWatcherUtils.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_AvailableMemoryWatcherUtils_h
   8 #define mozilla_AvailableMemoryWatcherUtils_h
   9
  10 #include "mozilla/Attributes.h"
  11 #include "nsISupportsUtils.h"  // For nsresult
  12
  13 namespace mozilla {
  14
  15 struct MemoryInfo {
  16   unsigned long memTotal;
  17   unsigned long memAvailable;
  18 };
  19 // Check /proc/meminfo for low memory. Largely C method for reading
  20 // /proc/meminfo.
  21 MOZ_MAYBE_UNUSED
  22 static nsresult ReadMemoryFile(const char* meminfoPath, MemoryInfo& aResult) {
  23   FILE* fd;
  24   if ((fd = fopen(meminfoPath, "r")) == nullptr) {
  25     // Meminfo somehow unreachable
  26     return NS_ERROR_FAILURE;
  27   }
  28
  29   char buff[128];
  30
  31   /* The first few lines of meminfo look something like this:
  32    * MemTotal:       65663448 kB
  33    * MemFree:        57368112 kB
  34    * MemAvailable:   61852700 kB
  35    * We mostly care about the available versus the total. We calculate our
  36    * memory thresholds using this, and when memory drops below 5% we consider
  37    * this to be a memory pressure event. In practice these lines aren't
  38    * necessarily in order, but we can simply search for MemTotal
  39    * and MemAvailable.
  40    */
  41   char namebuffer[20];
  42   while ((fgets(buff, sizeof(buff), fd)) != nullptr) {
  43     if (strstr(buff, "MemTotal:")) {
  44       sscanf(buff, "%s %lu ", namebuffer, &aResult.memTotal);
  45     }
  46     if (strstr(buff, "MemAvailable:")) {
  47       sscanf(buff, "%s %lu ", namebuffer, &aResult.memAvailable);
  48     }
  49   }
  50   fclose(fd);
  51   return NS_OK;
  52 }
  53
  54 }  // namespace mozilla
  55
  56 #endif  // ifndef mozilla_AvailableMemoryWatcherUtils_h