Merge pull request #794 from pagespeed/oschaaf-ipro-race

IPRO: Fix a race in processing writes() from NgxBaseFetch

src/ngx_base_fetch.cc

@@ -39,7 +39,7 @@ NgxBaseFetch::NgxBaseFetch(ngx_http_request_t* r, int pipe_fd,
       last_buf_sent_(false),
       pipe_fd_(pipe_fd),
       references_(2),
-      handle_error_(true),
+      ipro_lookup_(false),
       preserve_caching_headers_(preserve_caching_headers) {
   if (pthread_mutex_init(&mutex_, NULL)) CHECK(0);
 }
@@ -137,14 +137,20 @@ void NgxBaseFetch::HandleHeadersComplete() {
   int status_code = response_headers()->status_code();
   bool status_ok = (status_code != 0) && (status_code < 400);
 
-  if (status_ok || handle_error_) {
+  if (!ipro_lookup_ || status_ok) {
     // If this is a 404 response we need to count it in the stats.
     if (response_headers()->status_code() == HttpStatus::kNotFound) {
       server_context_->rewrite_stats()->resource_404_count()->Add(1);
     }
   }
 
+  // For the IPRO lookup, supress notification of the nginx side here.
+  // If we send both this event and the one from done, nasty stuff will happen
+  // if we loose the race with with the nginx side destructing this base fetch
+  // instance (and thereby clearing the byte and its pending extraneous event.
+  if (!ipro_lookup_) {
     RequestCollection();  // Headers available.
+  }
 }
 
 bool NgxBaseFetch::HandleFlush(MessageHandler* handler) {

src/ngx_base_fetch.h

@@ -79,7 +79,7 @@ class NgxBaseFetch : public AsyncFetch {
 
   // Called by nginx when it's done with us.
   void Release();
-  void set_handle_error(bool x) { handle_error_ = x; }
+  void set_ipro_lookup(bool x) { ipro_lookup_ = x; }
 
  private:
   virtual bool HandleWrite(const StringPiece& sp, MessageHandler* handler);
@@ -117,7 +117,7 @@ class NgxBaseFetch : public AsyncFetch {
   // decremented once when Done() is called and once when Release() is called.
   int references_;
   pthread_mutex_t mutex_;
-  bool handle_error_;
+  bool ipro_lookup_;
   PreserveCachingHeaders preserve_caching_headers_;
 
   DISALLOW_COPY_AND_ASSIGN(NgxBaseFetch);

src/ngx_pagespeed.cc

@@ -2022,7 +2022,7 @@ ngx_int_t ps_resource_handler(ngx_http_request_t* r,
         url_string.c_str());
 
     ctx->in_place = true;
-    ctx->base_fetch->set_handle_error(false);
+    ctx->base_fetch->set_ipro_lookup(true);
     ctx->driver->FetchInPlaceResource(
         url, false /* proxy_mode */, ctx->base_fetch);