Threads: offloading of temp files writing to thread pools.

The ngx_thread_write_chain_to_file() function introduced, which
uses ngx_file_t thread_handler, thread_ctx and thread_task fields.
The task context structure (ngx_thread_file_ctx_t) is the same for
both reading and writing, and can be safely shared as long as
operations are serialized.

The task->handler field is now always set (and not only when task is
allocated), as the same task can be used with different handlers.

The thread_write flag is introduced in the ngx_temp_file_t structure
to explicitly enable use of ngx_thread_write_chain_to_file() in
ngx_write_chain_to_temp_file() when supported by caller.

In collaboration with Valentin Bartenev.

2 files changed, 10 insertions, 0 deletions

diff --git a/src/core/ngx_file.c b/src/core/ngx_file.c
index 3ebd73d8b..2dc222865 100644
--- a/src/core/ngx_file.c
+++ b/src/core/ngx_file.c
@@ -124,6 +124,15 @@ ngx_write_chain_to_temp_file(ngx_temp_file_t *tf, ngx_chain_t *chain)
         }
     }
 
+#if (NGX_THREADS && NGX_HAVE_PWRITEV)
+
+    if (tf->thread_write) {
+        return ngx_thread_write_chain_to_file(&tf->file, chain, tf->offset,
+                                              tf->pool);
+    }
+
+#endif
+
     return ngx_write_chain_to_file(&tf->file, chain, tf->offset, tf->pool);
 }
 
diff --git a/src/core/ngx_file.h b/src/core/ngx_file.h
index aeb6c0cb2..5f8228b7b 100644
--- a/src/core/ngx_file.h
+++ b/src/core/ngx_file.h
@@ -78,6 +78,7 @@ typedef struct {
     unsigned                   log_level:8;
     unsigned                   persistent:1;
     unsigned                   clean:1;
+    unsigned                   thread_write:1;
 } ngx_temp_file_t;