init ssl roots only once

src/php/ext/grpc/channel_credentials.c

@@ -100,6 +100,17 @@ PHP_METHOD(ChannelCredentials, setDefaultRootsPem) {
   memcpy(default_pem_root_certs, pem_roots, pem_roots_length + 1);
 }
 
+/**
+ * if default roots pem is set
+ * @return TRUE/FALSE
+ */
+PHP_METHOD(ChannelCredentials, isDefaultRootsPemSet) {
+  if (default_pem_root_certs) {
+    RETURN_TRUE;
+  }
+  RETURN_FALSE;
+}
+
 /**
  * Create a default channel credentials object.
  * @return ChannelCredentials The new default channel credentials object
@@ -214,6 +225,9 @@ ZEND_BEGIN_ARG_INFO_EX(arginfo_setDefaultRootsPem, 0, 0, 1)
   ZEND_ARG_INFO(0, pem_roots)
 ZEND_END_ARG_INFO()
 
+ZEND_BEGIN_ARG_INFO_EX(arginfo_isDefaultRootsPemSet, 0, 0, 0)
+ZEND_END_ARG_INFO()
+
 ZEND_BEGIN_ARG_INFO_EX(arginfo_createDefault, 0, 0, 0)
 ZEND_END_ARG_INFO()
 
@@ -234,6 +248,8 @@ ZEND_END_ARG_INFO()
 static zend_function_entry channel_credentials_methods[] = {
   PHP_ME(ChannelCredentials, setDefaultRootsPem, arginfo_setDefaultRootsPem,
          ZEND_ACC_PUBLIC | ZEND_ACC_STATIC)
+  PHP_ME(ChannelCredentials, isDefaultRootsPemSet, arginfo_isDefaultRootsPemSet,
+         ZEND_ACC_PUBLIC | ZEND_ACC_STATIC)
   PHP_ME(ChannelCredentials, createDefault, arginfo_createDefault,
          ZEND_ACC_PUBLIC | ZEND_ACC_STATIC)
   PHP_ME(ChannelCredentials, createSsl, arginfo_createSsl,

src/php/lib/Grpc/BaseStub.php

@@ -43,10 +43,12 @@ class BaseStub
      */
     public function __construct($hostname, $opts, $channel = null)
     {
+        if (!ChannelCredentials::isDefaultRootsPemSet()) {
             $ssl_roots = file_get_contents(
                 dirname(__FILE__).'/../../../../etc/roots.pem'
             );
 	    ChannelCredentials::setDefaultRootsPem($ssl_roots);
+        }
 
         $this->hostname = $hostname;
         $this->update_metadata = null;