Only show a single mlock() error, to avoid flooding the log

contrib/epee/src/mlocker.cpp

@@ -38,6 +38,12 @@
 #include "syncobj.h"
 #include "mlocker.h"
 
+#include <atomic>
+
+// did an mlock operation previously fail? we only
+// want to log an error once and be done with it
+static std::atomic<bool> previously_failed{ false };
+
 static size_t query_page_size()
 {
 #if defined HAVE_MLOCK
@@ -59,8 +65,8 @@ static void do_lock(void *ptr, size_t len)
 {
 #if defined HAVE_MLOCK
   int ret = mlock(ptr, len);
-  if (ret < 0)
-    MERROR("Error locking page at " << ptr << ": " << strerror(errno));
+  if (ret < 0 && !previously_failed.exchange(true))
+    MERROR("Error locking page at " << ptr << ": " << strerror(errno) << ", subsequent mlock errors will be silenced");
 #else
 #warning Missing do_lock implementation
 #endif
@@ -70,7 +76,10 @@ static void do_unlock(void *ptr, size_t len)
 {
 #if defined HAVE_MLOCK
   int ret = munlock(ptr, len);
-  if (ret < 0)
+  // check whether we previously failed, but don't set it, this is just
+  // to pacify the errors of mlock()ing failed, in which case unlocking
+  // is also not going to work of course
+  if (ret < 0 && !previously_failed.load())
     MERROR("Error unlocking page at " << ptr << ": " << strerror(errno));
 #else
 #warning Missing implementation of page size detection