SERVER-46382 Add exception handler so log statements do not throw.

Exceptions during log is fatal in debug builds only

2 files changed, 33 insertions, 0 deletions

diff --git a/src/mongo/logv2/log_manager.cpp b/src/mongo/logv2/log_manager.cpp
index 8f8453417e2..b5fc193ace3 100644
--- a/src/mongo/logv2/log_manager.cpp
+++ b/src/mongo/logv2/log_manager.cpp
@@ -29,8 +29,13 @@
 
 #include "mongo/platform/basic.h"
 
+#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kDefault
+
 #include "mongo/logv2/log_manager.h"
 
+#include <boost/log/core.hpp>
+
+#include "mongo/logv2/log.h"
 #include "mongo/logv2/log_domain.h"
 #include "mongo/logv2/log_domain_global.h"
 
@@ -46,6 +51,28 @@ struct LogManager::Impl {
 
 LogManager::LogManager() {
     _impl = std::make_unique<Impl>();
+
+    boost::log::core::get()->set_exception_handler([]() {
+        thread_local uint32_t depth = 0;
+        auto depthGuard = makeGuard([]() { --depth; });
+        ++depth;
+        // Try and log that we failed to log
+        if (depth == 1) {
+            try {
+                throw;
+            } catch (...) {
+                LOGV2(4638200,
+                      "Exception during log, message not written to stream",
+                      "exception"_attr = exceptionToStatus());
+            }
+        }
+
+        // Logging exceptions are fatal in debug builds. Guard ourselves from additional logging
+        // during the assert that might also fail
+        if (kDebugBuild && depth <= 2) {
+            dassert(false, "Exception during log");
+        }
+    });
 }
 
 LogManager::~LogManager() {}
diff --git a/src/mongo/logv2/log_test_v2.cpp b/src/mongo/logv2/log_test_v2.cpp
index 12a592975d9..f0ac7e3218f 100644
--- a/src/mongo/logv2/log_test_v2.cpp
+++ b/src/mongo/logv2/log_test_v2.cpp
@@ -245,6 +245,12 @@ TEST_F(LogTestV2, Basic) {
     // Text formatter selects format string
     LOGV2(20084, "fmtstr {name}", "msgstr", "name"_attr = 1);
     ASSERT_EQUALS(lines.back(), "fmtstr 1");
+
+    // Test that logging exceptions does not propagate out to user code in release builds
+    if (!kDebugBuild) {
+        LOGV2(4638203, "mismatch {name}", "not_name"_attr = 1);
+        ASSERT(StringData(lines.back()).startsWith("Exception during log"_sd));
+    }
 }
 
 TEST_F(LogTestV2, Types) {