From bc3c0fa93622e498d07cd01f6f40e3d5a9120c05 Mon Sep 17 00:00:00 2001
From: Tom <tomut@yahoo.com>
Date: Sun, 3 Jan 2021 10:08:51 -0700
Subject: [PATCH] LibCore: Allow caching and reusing the ProcFS file
 descriptors

Because ProcFS will refresh the data upon seek to 0, we can re-use
the same file descriptor. This saves us from having to open it every
time, but it also reduces the odds that we are unable to open a new
file descriptor due to low memory conditions.
---
 Libraries/LibCore/ProcessStatisticsReader.cpp | 25 ++++++++++++++-----
 Libraries/LibCore/ProcessStatisticsReader.h   |  2 ++
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/Libraries/LibCore/ProcessStatisticsReader.cpp b/Libraries/LibCore/ProcessStatisticsReader.cpp
index 53312872af..566053d3af 100644
--- a/Libraries/LibCore/ProcessStatisticsReader.cpp
+++ b/Libraries/LibCore/ProcessStatisticsReader.cpp
@@ -37,17 +37,24 @@ namespace Core {
 
 HashMap<uid_t, String> ProcessStatisticsReader::s_usernames;
 
-Optional<HashMap<pid_t, Core::ProcessStatistics>> ProcessStatisticsReader::get_all()
+Optional<HashMap<pid_t, Core::ProcessStatistics>> ProcessStatisticsReader::get_all(RefPtr<Core::File>& proc_all_file)
 {
-    auto file = Core::File::construct("/proc/all");
-    if (!file->open(Core::IODevice::ReadOnly)) {
-        fprintf(stderr, "ProcessStatisticsReader: Failed to open /proc/all: %s\n", file->error_string());
-        return {};
+    if (proc_all_file) {
+        if (!proc_all_file->seek(0, Core::File::SeekMode::SetPosition)) {
+            fprintf(stderr, "ProcessStatisticsReader: Failed to refresh /proc/all: %s\n", proc_all_file->error_string());
+            return {};
+        }
+    } else {
+        proc_all_file = Core::File::construct("/proc/all");
+        if (!proc_all_file->open(Core::IODevice::ReadOnly)) {
+            fprintf(stderr, "ProcessStatisticsReader: Failed to open /proc/all: %s\n", proc_all_file->error_string());
+            return {};
+        }
     }
 
     HashMap<pid_t, Core::ProcessStatistics> map;
 
-    auto file_contents = file->read_all();
+    auto file_contents = proc_all_file->read_all();
     auto json = JsonValue::from_string(file_contents);
     if (!json.has_value())
         return {};
@@ -112,6 +119,12 @@ Optional<HashMap<pid_t, Core::ProcessStatistics>> ProcessStatisticsReader::get_a
     return map;
 }
 
+Optional<HashMap<pid_t, Core::ProcessStatistics>> ProcessStatisticsReader::get_all()
+{
+    RefPtr<Core::File> proc_all_file;
+    return get_all(proc_all_file);
+}
+
 String ProcessStatisticsReader::username_from_uid(uid_t uid)
 {
     if (s_usernames.is_empty()) {
diff --git a/Libraries/LibCore/ProcessStatisticsReader.h b/Libraries/LibCore/ProcessStatisticsReader.h
index 02519e83f6..b6e506cd9d 100644
--- a/Libraries/LibCore/ProcessStatisticsReader.h
+++ b/Libraries/LibCore/ProcessStatisticsReader.h
@@ -28,6 +28,7 @@
 
 #include <AK/HashMap.h>
 #include <AK/String.h>
+#include <LibCore/File.h>
 #include <unistd.h>
 
 namespace Core {
@@ -86,6 +87,7 @@ struct ProcessStatistics {
 
 class ProcessStatisticsReader {
 public:
+    static Optional<HashMap<pid_t, Core::ProcessStatistics>> get_all(RefPtr<Core::File>&);
     static Optional<HashMap<pid_t, Core::ProcessStatistics>> get_all();
 
 private: