SERVER-34960 Add MONGO_FAIL_POINT_BLOCK_IF

It's sometimes useful to be able to check a pre-condition on a fail
point without manipulating the fail point state (decrementing nTimes for
instance).

Adding a callable to shouldFailOpenBlock and shouldFail, and threading
that through a new block macro MONGO_FAIL_POINT_BLOCK_IF, allows for
observation of the fail point payload and a chance to abort without
extra overhead if the fail point is disabled.

1 files changed, 6 insertions, 1 deletions

diff --git a/src/mongo/util/fail_point.cpp b/src/mongo/util/fail_point.cpp
index 75be5f48231..4ba84bee3ec 100644
--- a/src/mongo/util/fail_point.cpp
+++ b/src/mongo/util/fail_point.cpp
@@ -141,13 +141,18 @@ void FailPoint::disableFailPoint() {
     } while (expectedCurrentVal != currentVal);
 }
 
-FailPoint::RetCode FailPoint::slowShouldFailOpenBlock() {
+FailPoint::RetCode FailPoint::slowShouldFailOpenBlock(
+    stdx::function<bool(const BSONObj&)> cb) noexcept {
     ValType localFpInfo = _fpInfo.addAndFetch(1);
 
     if ((localFpInfo & ACTIVE_BIT) == 0) {
         return slowOff;
     }
 
+    if (cb && !cb(getData())) {
+        return userIgnored;
+    }
+
     switch (_mode) {
         case alwaysOn:
             return slowOn;