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
diff --git a/libprocessgroup/processgroup.cpp b/libprocessgroup/processgroup.cpp
index ae9914d..a021594 100644
--- a/libprocessgroup/processgroup.cpp
+++ b/libprocessgroup/processgroup.cpp
@@ -542,6 +542,15 @@
     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);