Constify return value of get*ExceptionStackTraceStack

Summary: It's a read-only interface.

Reviewed By: philippv, luciang

Differential Revision: D19199710

fbshipit-source-id: 5e900edd35640cded45e6376eb0b81b9036bd792

folly/experimental/exception_tracer/ExceptionStackTraceLib.cpp

@@ -36,10 +36,10 @@ FOLLY_TLS StackTraceStack caughtExceptions;
 } // namespace
 
 // These functions are exported and may be found via dlsym(RTLD_NEXT, ...)
-extern "C" StackTraceStack* getUncaughtExceptionStackTraceStack() {
+extern "C" const StackTraceStack* getUncaughtExceptionStackTraceStack() {
   return invalid ? nullptr : &uncaughtExceptions;
 }
-extern "C" StackTraceStack* getCaughtExceptionStackTraceStack() {
+extern "C" const StackTraceStack* getCaughtExceptionStackTraceStack() {
   return invalid ? nullptr : &caughtExceptions;
 }
 

folly/experimental/exception_tracer/ExceptionTracer.cpp

@@ -37,9 +37,9 @@ using namespace ::folly::symbolizer;
 using namespace __cxxabiv1;
 
 extern "C" {
-StackTraceStack* getCaughtExceptionStackTraceStack(void)
+const StackTraceStack* getCaughtExceptionStackTraceStack(void)
     __attribute__((__weak__));
-typedef StackTraceStack* (*GetCaughtExceptionStackTraceStackType)();
+typedef const StackTraceStack* (*GetCaughtExceptionStackTraceStackType)();
 GetCaughtExceptionStackTraceStackType getCaughtExceptionStackTraceStackFn;
 }
 
@@ -150,7 +150,7 @@ std::vector<ExceptionInfo> getCurrentExceptions() {
     return exceptions;
   }
 
-  StackTraceStack* traceStack = nullptr;
+  const StackTraceStack* traceStack = nullptr;
   if (!getCaughtExceptionStackTraceStackFn) {
     static bool logged = false;
     if (!logged) {
@@ -167,7 +167,7 @@ std::vector<ExceptionInfo> getCurrentExceptions() {
     }
   }
 
-  StackTrace* trace = traceStack ? traceStack->top() : nullptr;
+  const StackTrace* trace = traceStack ? traceStack->top() : nullptr;
   while (currentException) {
     ExceptionInfo info;
     // Dependent exceptions (thrown via std::rethrow_exception) aren't

folly/experimental/exception_tracer/StackTrace.cpp

@@ -103,10 +103,21 @@ StackTrace* StackTraceStack::top() {
   return state_[kTopIdx];
 }
 
+const StackTrace* StackTraceStack::top() const {
+  checkGuard();
+  return state_[kTopIdx];
+}
+
 StackTrace* StackTraceStack::next(StackTrace* p) {
   checkGuard();
   assert(p);
   return static_cast<Node*>(p)->next;
 }
+
+const StackTrace* StackTraceStack::next(const StackTrace* p) const {
+  checkGuard();
+  assert(p);
+  return static_cast<const Node*>(p)->next;
+}
 } // namespace exception_tracer
 } // namespace folly

folly/experimental/exception_tracer/StackTrace.h

@@ -76,12 +76,14 @@ class StackTraceStack {
    * Return the top stack trace, or nullptr if the stack is empty.
    */
   StackTrace* top();
+  const StackTrace* top() const;
 
   /**
    * Return the stack trace following p, or nullptr if p is the bottom of
    * the stack.
    */
   StackTrace* next(StackTrace* p);
+  const StackTrace* next(const StackTrace* p) const;
 
  private:
   static constexpr size_t kTopIdx = kIsDebug ? 1 : 0;