libprocessgroup: Add sendSignalToProcessGroup

Add a function which sends signals to all members of a process group,
but does not wait for the processes to exit, or for the associated
cgroup to be removed.

Bug: 274646058
Ignore-AOSP-First: Dependency of ActivityManager change which developed on interal git_master
Test: Force-stop of chrome with 15 tabs completes ~500ms faster
Test: Full Play store update causes no ANR
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:d87b6018d25cbbd33b345dc58c634718bf5d0def)
Merged-In: I37dbdecb3394101abbee8495e71f6912b3c031f5
Change-Id: I37dbdecb3394101abbee8495e71f6912b3c031f5

NOTE FOR REVIEWERS - original patch and result patch are not identical.
PLEASE REVIEW CAREFULLY.
Diffs between the patches:
37,6 +537,15 @@
     return KillProcessGroup(uid, initialPid, signal, 0 /*retries*/, max_processes);
 }
 
+int sendSignalToProcessGroup(uid_t uid, int initialPid, int signal) {
+    std::string hierarchy_root_path;
+    if (CgroupsAvailable()) {
+        CgroupGetControllerPath(CGROUPV2_CONTROLLER_NAME, &hierarchy_root_path);
+    }
+    const char* cgroup = hierarchy_root_path.c_str();
+    return DoKillProcessGroupOnce(cgroup, uid, initialPid, signal);
+}
+
 static int createProcessGroupInternal(uid_t uid, int initialPid, std::string cgroup,
                                       bool activate_controllers) {
     auto uid_path = ConvertUidToPath(cgroup.c_str(), uid);

Original patch:
From d87b6018 Mon Sep 17 00:00:00 2001
From: T.J. Mercier <tjmercier@google.com>
Date: Tue, 04 Apr 2023 18:41:13 +0000
Subject: [PATCH] libprocessgroup: Add sendSignalToProcessGroup

Add a function which sends signals to all members of a process group,
but does not wait for the processes to exit, or for the associated
cgroup to be removed.

Bug: 274646058
Ignore-AOSP-First: Dependency of ActivityManager change which developed on interal git_master
Test: Force-stop of chrome with 15 tabs completes ~500ms faster
Test: Full Play store update causes no ANR
Change-Id: I37dbdecb3394101abbee8495e71f6912b3c031f5
---

diff --git a/libprocessgroup/include/processgroup/processgroup.h b/libprocessgroup/include/processgroup/processgroup.h
index 8fa9fd5..48bc0b7 100644
--- a/libprocessgroup/include/processgroup/processgroup.h
+++ b/libprocessgroup/include/processgroup/processgroup.h
@@ -76,6 +76,11 @@
 // that it only returns 0 in the case that the cgroup exists and it contains no processes.
 int killProcessGroupOnce(uid_t uid, int initialPid, int signal, int* max_processes = nullptr);
 
+// Sends the provided signal to all members of a process group, but does not wait for processes to
+// exit, or for the cgroup to be removed. Callers should also ensure that killProcessGroup is called
+// later to ensure the cgroup is fully removed, otherwise system resources may leak.
+int sendSignalToProcessGroup(uid_t uid, int initialPid, int signal);
+
 int createProcessGroup(uid_t uid, int initialPid, bool memControl = false);
 
 // Set various properties of a process group. For these functions to work, the process group must

Change-Id: Ie479348dee8e8092b1959927a1143009632d3914