Don't use malloc from pcntl_signal_handler

Not kosher.

hphp/runtime/ext/ext_process.cpp

@@ -20,6 +20,7 @@
 #include "hphp/runtime/ext/ext_function.h"
 #include "hphp/runtime/base/string_buffer.h"
 #include "hphp/runtime/base/zend_string.h"
+#include "hphp/runtime/base/thread_init_fini.h"
 #include <unistd.h>
 #include <fcntl.h>
 #include <signal.h>
@@ -281,6 +282,16 @@ public:
 };
 IMPLEMENT_STATIC_REQUEST_LOCAL(SignalHandlers, s_signal_handlers);
 
+// We must register the s_signal_handlers RequestEventHandler
+// immediately: otherwise, pcntl_signal_handler might try to register
+// it while processing a signal, which means calling malloc to insert
+// it into various vectors and sets, which is not ok from a signal
+// handler.
+const InitFiniNode initSignalHandler(
+  [] { s_signal_handlers.get(); },
+  InitFiniNode::When::ThreadInit
+);
+
 static void pcntl_signal_handler(int signo) {
   if (signo > 0 && signo < _NSIG && !g_context.isNull()) {
     s_signal_handlers->signaled[signo] = 1;