[PATCH] Processes that spawn other processes should wait for their children to exit before exiting due to a signal.

[Chris Bieneman]

Hi ddunbar,

If a process that spawns other processes (like the clang driver) gets killed via a SIGINT, it should wait until its children exit before returning from the signal handler. This prevents the child processes from getting re-parented, which causes problems for build systems that are the parent of clang processes.

http://reviews.llvm.org/D9420

Files:
  lib/Support/Unix/Program.inc

Index: lib/Support/Unix/Program.inc
===================================================================
--- lib/Support/Unix/Program.inc
+++ lib/Support/Unix/Program.inc
@@ -21,8 +21,10 @@
 #include "llvm/Config/config.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/FileSystem.h"
+#include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/Signals.h"
 #if HAVE_SYS_STAT_H
 #include <sys/stat.h>
 #endif
@@ -61,10 +63,14 @@
 #endif
 #endif
 
+#include <vector>
+
 namespace llvm {
 
 using namespace sys;
 
+static ManagedStatic<std::vector<ProcessInfo>> ChildPIDs;
+
 ProcessInfo::ProcessInfo() : Pid(0), ReturnCode(0) {}
 
 ErrorOr<std::string> sys::findProgramByName(StringRef Name,
@@ -177,6 +183,13 @@
 
 }
 
+static void WaitForChildren(void *) {
+  if(ChildPIDs.isConstructed())
+    for (auto PI : *ChildPIDs) 
+      Wait(PI, 0, true, nullptr);
+  ChildPIDs->clear();
+}
+
 static bool Execute(ProcessInfo &PI, StringRef Program, const char **args,
                     const char **envp, const StringRef **redirects,
                     unsigned memoryLimit, std::string *ErrMsg) {
@@ -187,6 +200,8 @@
     return false;
   }
 
+  AddSignalHandler(WaitForChildren, nullptr);
+
   // If this OS has posix_spawn and there is no memory limit being implied, use
   // posix_spawn.  It is more efficient than fork/exec.
 #ifdef HAVE_POSIX_SPAWN

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