[libmicrohttpd] 11/13: Added new daemon flag MHD_USE_NO_THREAD_SAFETY

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karlson2k pushed a commit to branch master
in repository libmicrohttpd.

commit b05555f8372fd848698d87133d8ed194820ede1e
Author: Evgeny Grin (Karlson2k) <k2k@narod.ru>
AuthorDate: Tue Nov 21 17:32:34 2023 +0300

    Added new daemon flag MHD_USE_NO_THREAD_SAFETY
    
    Do not assume anymore single-threaded environment if external polling
    is used.
    The application is free to use multiple threads if MHD in the external
    polling mode.
    The new flag could be used to disable some thread-safety in MHD to
    improve single-thread processing speed and resources usage. Basically
    the new flag restores the old behaviour for external polling mode.
---
 src/include/microhttpd.h  | 16 ++++++++++++++--
 src/microhttpd/daemon.c   | 29 +++++++++++++++--------------
 src/microhttpd/internal.h | 11 +++++++++++
 3 files changed, 40 insertions(+), 16 deletions(-)

diff --git a/src/include/microhttpd.h b/src/include/microhttpd.h
index e1d12645..13bd2cbf 100644
--- a/src/include/microhttpd.h
+++ b/src/include/microhttpd.h
@@ -96,7 +96,7 @@ extern "C"
  * they are parsed as decimal numbers.
  * Example: 0x01093001 = 1.9.30-1.
  */
-#define MHD_VERSION 0x00097706
+#define MHD_VERSION 0x00097707
 
 /* If generic headers don't work on your platform, include headers
    which define 'va_list', 'size_t', 'ssize_t', 'intptr_t', 'off_t',
@@ -1531,7 +1531,19 @@ enum MHD_FLAG
    * Flag set to enable TLS 1.3 early data.  This has
    * security implications, be VERY careful when using this.
    */
-  MHD_USE_INSECURE_TLS_EARLY_DATA = 1U << 18
+  MHD_USE_INSECURE_TLS_EARLY_DATA = 1U << 18,
+
+  /**
+   * Indicates that MHD daemon will be used by application in single-threaded
+   * mode only.  When this flag is set then application must call any MHD
+   * function only within a single thread.
+   * This flag turns off some internal thread-safety and allows MHD making
+   * some of the internal optimisations suitable only for single-threaded
+   * environment.
+   * Not compatible with #MHD_USE_INTERNAL_POLLING_THREAD.
+   * @note Available since #MHD_VERSION 0x00097707
+   */
+  MHD_USE_NO_THREAD_SAFETY = 1U << 19
 
 };
 
diff --git a/src/microhttpd/daemon.c b/src/microhttpd/daemon.c
index 98a3a4c8..27cf3534 100644
--- a/src/microhttpd/daemon.c
+++ b/src/microhttpd/daemon.c
@@ -3152,9 +3152,9 @@ internal_add_connection (struct MHD_Daemon *daemon,
     return MHD_NO;
 
   if ((external_add) &&
-      MHD_D_IS_USING_THREADS_ (daemon))
+      MHD_D_IS_THREAD_SAFE_ (daemon))
   {
-    /* Connection is added externally and MHD is handling its own threads. */
+    /* Connection is added externally and MHD is thread safe mode. */
     MHD_mutex_lock_chk_ (&daemon->new_connections_mutex);
     DLL_insert (daemon->new_connections_head,
                 daemon->new_connections_tail,
@@ -3186,7 +3186,7 @@ new_connections_list_process_ (struct MHD_Daemon *daemon)
   struct MHD_Connection *local_head;
   struct MHD_Connection *local_tail;
   mhd_assert (daemon->have_new);
-  mhd_assert (MHD_D_IS_USING_THREADS_ (daemon));
+  mhd_assert (MHD_D_IS_THREAD_SAFE_ (daemon));
 
   /* Detach DL-list of new connections from the daemon for
    * following local processing. */
@@ -3621,8 +3621,8 @@ MHD_add_connection (struct MHD_Daemon *daemon,
   bool sk_spipe_supprs;
   struct sockaddr_storage addrstorage;
 
-  /* NOT thread safe with internal thread. TODO: fix thread safety. */
-  if ((! MHD_D_IS_USING_THREADS_ (daemon)) &&
+  /* TODO: fix atomic value reading */
+  if ((! MHD_D_IS_THREAD_SAFE_ (daemon)) &&
       (daemon->connection_limit <= daemon->connections))
     MHD_cleanup_connections (daemon);
 
@@ -7667,7 +7667,12 @@ MHD_start_daemon_va (unsigned int flags,
     return NULL;
 #endif /* ! UPGRADE_SUPPORT */
   }
-#ifndef MHD_USE_THREADS
+#ifdef MHD_USE_THREADS
+  if ((MHD_USE_NO_THREAD_SAFETY | MHD_USE_INTERNAL_POLLING_THREAD) ==
+      ((MHD_USE_NO_THREAD_SAFETY | MHD_USE_INTERNAL_POLLING_THREAD)
+       & *pflags))
+    return NULL; /* Cannot be thread-unsafe with multiple threads */
+#else  /* ! MHD_USE_THREADS */
   if (0 != (*pflags & MHD_USE_INTERNAL_POLLING_THREAD))
     return NULL;
 #endif /* ! MHD_USE_THREADS */
@@ -7707,9 +7712,9 @@ MHD_start_daemon_va (unsigned int flags,
 #endif
   }
 
-  if (0 == (*pflags & MHD_USE_INTERNAL_POLLING_THREAD))
-    *pflags = (*pflags & ~((enum MHD_FLAG) MHD_USE_ITC)); /* useless if we are 
using 'external' select */
-  else
+  if (0 != (*pflags & MHD_USE_NO_THREAD_SAFETY))
+    *pflags = (*pflags & ~((enum MHD_FLAG) MHD_USE_ITC)); /* useless in 
single-threaded environment */
+  else if (0 != (*pflags & MHD_USE_INTERNAL_POLLING_THREAD))
   {
 #ifdef HAVE_LISTEN_SHUTDOWN
     if (0 != (*pflags & MHD_USE_NO_LISTEN_SOCKET))
@@ -9426,12 +9431,8 @@ MHD_get_daemon_info (struct MHD_Daemon *daemon,
     return NULL;
 #endif /* ! EPOLL_SUPPORT */
   case MHD_DAEMON_INFO_CURRENT_CONNECTIONS:
-    if (! MHD_D_IS_USING_THREADS_ (daemon))
-    {
-      /* Assume that MHD_run() in not called in other thread
-       * at the same time. */
+    if (! MHD_D_IS_THREAD_SAFE_ (daemon))
       MHD_cleanup_connections (daemon);
-    }
 #if defined(MHD_USE_POSIX_THREADS) || defined(MHD_USE_W32_THREADS)
     else if (daemon->worker_pool)
     {
diff --git a/src/microhttpd/internal.h b/src/microhttpd/internal.h
index 4113e66d..667b6071 100644
--- a/src/microhttpd/internal.h
+++ b/src/microhttpd/internal.h
@@ -2551,6 +2551,12 @@ struct MHD_Daemon
  */
 #define MHD_D_IS_USING_THREAD_PER_CONN_(d) \
   (0 != ((d)->options & MHD_USE_THREAD_PER_CONNECTION))
+
+/**
+ * Check whether the @a d daemon has thread-safety enabled.
+ */
+#define MHD_D_IS_THREAD_SAFE_(d) \
+  (0 == ((d)->options & MHD_USE_NO_THREAD_SAFETY))
 #else  /* ! MHD_USE_THREADS */
 /**
  * Checks whether the @a d daemon is using internal polling thread
@@ -2560,6 +2566,11 @@ struct MHD_Daemon
  * Checks whether the @a d daemon is using thread-per-connection mode
  */
 #define MHD_D_IS_USING_THREAD_PER_CONN_(d) ((void) d, 0)
+
+/**
+ * Check whether the @a d daemon has thread-safety enabled.
+ */
+#define MHD_D_IS_THREAD_SAFE_(d) ((void) d, 0)
 #endif /* ! MHD_USE_THREADS */
 
 #ifdef HAS_FD_SETSIZE_OVERRIDABLE

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