1 files changed, 56 insertions, 0 deletions
diff --git a/xpcom/base/AvailableMemoryWatcherUtils.h b/xpcom/base/AvailableMemoryWatcherUtils.h
new file mode 100644
index 0000000000..2d70fe5fd0
--- /dev/null
+++ b/xpcom/base/AvailableMemoryWatcherUtils.h
@@ -0,0 +1,56 @@
+/* -*- 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 mozilla_AvailableMemoryWatcherUtils_h
+#define mozilla_AvailableMemoryWatcherUtils_h
+
+#include "mozilla/Attributes.h"
+#include "nsISupportsUtils.h"  // For nsresult
+
+namespace mozilla {
+
+struct MemoryInfo {
+  unsigned long memTotal;
+  unsigned long memAvailable;
+};
+// Check /proc/meminfo for low memory. Largely C method for reading
+// /proc/meminfo.
+MOZ_MAYBE_UNUSED
+static nsresult ReadMemoryFile(const char* meminfoPath, MemoryInfo& aResult) {
+  FILE* fd;
+  if ((fd = fopen(meminfoPath, "r")) == nullptr) {
+    // Meminfo somehow unreachable
+    return NS_ERROR_FAILURE;
+  }
+
+  char buff[128];
+
+  /* The first few lines of meminfo look something like this:
+   * MemTotal:       65663448 kB
+   * MemFree:        57368112 kB
+   * MemAvailable:   61852700 kB
+   * We mostly care about the available versus the total. We calculate our
+   * memory thresholds using this, and when memory drops below 5% we consider
+   * this to be a memory pressure event. In practice these lines aren't
+   * necessarily in order, but we can simply search for MemTotal
+   * and MemAvailable.
+   */
+  char namebuffer[20];
+  while ((fgets(buff, sizeof(buff), fd)) != nullptr) {
+    if (strstr(buff, "MemTotal:")) {
+      sscanf(buff, "%s %lu ", namebuffer, &aResult.memTotal);
+    }
+    if (strstr(buff, "MemAvailable:")) {
+      sscanf(buff, "%s %lu ", namebuffer, &aResult.memAvailable);
+    }
+  }
+  fclose(fd);
+  return NS_OK;
+}
+
+}  // namespace mozilla
+
+#endif  // ifndef mozilla_AvailableMemoryWatcherUtils_h