add received_danger

Signed-off-by: Mattias Andrée <maandree@operamail.com>

3 files changed, 51 insertions, 12 deletions

diff --git a/doc/info/mds.texinfo b/doc/info/mds.texinfo
index 3c5e1ce..0d721b8 100644
--- a/doc/info/mds.texinfo
+++ b/doc/info/mds.texinfo
@@ -4157,6 +4157,16 @@ implementation if the server is multi-threaded. It sends
 the singal @code{signo} to all threads except the current
 thread.
 
+@item @code{received_danger} [(@code{int signo}) @arrow{} @code{void}]
+This function is called when a signal that signals the
+system is running out of memory has been received. The exact
+received signal is specified by the parameter @code{signo}.
+When this function is invoked, the server should free up
+all memory it can spare. If the server never has any memory
+that could be freed this function does not been to be
+overridden. If @code{server_characteristics.danger_is_deadly}
+is set, this function will never be called.
+
 @item @code{received_reexec} [(@code{int signo}) @arrow{} @code{void}]
 This function is called when a signal that signals the
 server to re-execute has been received. The exact
diff --git a/src/mds-base.c b/src/mds-base.c
index 4584670..3553c69 100644
--- a/src/mds-base.c
+++ b/src/mds-base.c
@@ -275,29 +275,32 @@ int __attribute__((weak)) server_initialised(void)
 }
 
 
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wsuggest-attribute=const"
 /**
- * This function is called when an intraprocess signal
- * that used to send a notification to a thread
+ * This function should be implemented by the actual server implementation
+ * if the server is multi-threaded
  * 
- * @param  signo  The signal that has been received
+ * Send a singal to all threads except the current thread
+ * 
+ * @param  signo  The signal
  */
-static void __attribute__((const)) received_noop(int signo)
+void __attribute__((weak)) signal_all(int signo)
 {
   (void) signo;
 }
 
 
-# pragma GCC diagnostic push
-# pragma GCC diagnostic ignored "-Wsuggest-attribute=const"
 /**
- * This function should be implemented by the actual server implementation
- * if the server is multi-threaded
+ * This function is called when a signal that
+ * signals that the system is running out of memory
+ * has been received
  * 
- * Send a singal to all threads except the current thread
+ * By default this function does not do anything
  * 
- * @param  signo  The signal
+ * @param  signo  The signal that has been received
  */
-void __attribute__((weak)) signal_all(int signo)
+void __attribute__((weak)) received_danger(int signo)
 {
   (void) signo;
 }
@@ -305,6 +308,21 @@ void __attribute__((weak)) signal_all(int signo)
 
 
 /**
+ * This function is called when an intraprocess signal
+ * that used to send a notification to a thread
+ * 
+ * @param  signo  The signal that has been received
+ */
+static void __attribute__((const)) received_noop(int signo)
+{
+  (void) signo;
+  /* This function is used rather than SIG_IGN because we
+   * want blocking functions to return with errno set to
+   * `EINTR` rather than continue blocking. */
+}
+
+
+/**
  * This function is called when a signal that
  * signals the server to re-exec has been received
  * 
@@ -611,7 +629,7 @@ int trap_signals(void)
   if (server_characteristics.danger_is_deadly && !is_immortal)
     { fail_if (xsigaction(SIGDANGER, commit_suicide) < 0); }
   else
-    { fail_if (xsigaction(SIGDANGER, SIG_IGN) < 0); }
+    { fail_if (xsigaction(SIGDANGER, received_danger) < 0); }
   
   return 0;
  pfail:
diff --git a/src/mds-base.h b/src/mds-base.h
index 1ea132a..0b5f85a 100644
--- a/src/mds-base.h
+++ b/src/mds-base.h
@@ -203,6 +203,17 @@ void signal_all(int signo); /* __attribute__((weak)) */
 
 /**
  * This function is called when a signal that
+ * signals that the system is running out of memory
+ * has been received
+ * 
+ * By default this function does not do anything
+ * 
+ * @param  signo  The signal that has been received
+ */
+void received_danger(int signo);
+
+/**
+ * This function is called when a signal that
  * signals the server to re-exec has been received
  * 
  * When this function is invoked, it should set `reexecing` and