Add DEFER macro, similar to go's defer
DEFER macro lets you run a block of code when exit from current scope.
Example use case:
1. Close a file descriptor when function returns
2. Call fclose()/lz4stream_close() routines before return
While these cases can be covered with unique ptr or custom RAII object,
inventing a new type for each usecase is somewhat cumbersome. So added
this macro to help.
Test: th
Bug: 206729162
Change-Id: I05d3b5df1bc31a451ef9f6328633acc06d547e6e
diff --git a/common/utils.cc b/common/utils.cc
index e47b70b..8b57075 100644
--- a/common/utils.cc
+++ b/common/utils.cc
@@ -63,7 +63,6 @@
using base::TimeDelta;
using std::min;
using std::numeric_limits;
-using std::pair;
using std::string;
using std::vector;
diff --git a/common/utils.h b/common/utils.h
index 4ff4050..a0a466d 100644
--- a/common/utils.h
+++ b/common/utils.h
@@ -38,6 +38,7 @@
#include <brillo/secure_blob.h>
#include "android-base/mapped_file.h"
+#include "android-base/scopeguard.h"
#include "google/protobuf/repeated_field.h"
#include "update_engine/common/action.h"
#include "update_engine/common/action_processor.h"
@@ -584,4 +585,25 @@
#define TEST_LT(_x, _y) TEST_OP(_x, _y, <)
#define TEST_GT(_x, _y) TEST_OP(_x, _y, >)
+// Macro for running a block of code before function exits.
+// Example:
+// DEFER {
+// fclose(hc);
+// hc = nullptr;
+// };
+// It works by creating a new local variable struct holding the lambda, the
+// destructor of that struct will invoke the lambda.
+
+constexpr struct {
+ template <typename F>
+ constexpr auto operator<<(F&& f) const noexcept {
+ return android::base::make_scope_guard(std::forward<F>(f));
+ }
+} deferrer;
+
+#define TOKENPASTE(x, y) x##y
+#define DEFER \
+ auto TOKENPASTE(_deferred_lambda_call, __COUNTER__) = deferrer \
+ << [&]() mutable
+
#endif // UPDATE_ENGINE_COMMON_UTILS_H_