Avoid wiping full error context on release

Reviewed-on: #25

CMakeLists.txt

@@ -158,10 +158,18 @@ add_custom_command(
   VERBATIM
 )
 
+# More than one library target consumes the generated sources below. Route
+# them through one explicit prerequisite so parallel Make builds cannot invoke
+# the same generator twice and interleave writes to errno.c.
+add_custom_target(akerror_generated
+  DEPENDS ${GENERATED_ERRNO_C} ${GENERATED_AKERROR_H}
+)
+
 add_library(akerror SHARED
   src/error.c
   ${GENERATED_ERRNO_C}
 )
+add_dependencies(akerror akerror_generated)
 
 target_include_directories(akerror PUBLIC
   $<BUILD_INTERFACE:${GENERATED_DIR}/include>
@@ -200,6 +208,32 @@ set_target_properties(akerror PROPERTIES
 akerr_instrument_for_coverage(akerror)
 akerr_instrument_for_sanitizers(akerror)
 
+# akerr_init() must terminate if it cannot reserve the library-owned status
+# band. The production table sizes are deliberately PRIVATE, so exercise that
+# otherwise unreachable startup failure with a second library target whose
+# private registries cannot accept even the first reservation. Keeping this a
+# distinct target is the test: no compile definition leaks into consumers or
+# weakens the production library.
+add_library(akerror_init_failure SHARED
+  src/error.c
+  ${GENERATED_ERRNO_C}
+)
+add_dependencies(akerror_init_failure akerror_generated)
+target_include_directories(akerror_init_failure PUBLIC
+  ${GENERATED_DIR}/include
+)
+target_compile_definitions(akerror_init_failure
+  PUBLIC AKERR_USE_STDLIB=${AKERR_USE_STDLIB}
+  PRIVATE AKERR_STATUS_NAME_SLOTS=8
+  PRIVATE AKERR_MAX_RESERVED_STATUS_RANGES=0
+  PRIVATE ${AKERR_THREADS_DEFINE}
+)
+if(AKERR_THREAD_SAFE)
+    target_link_libraries(akerror_init_failure PRIVATE Threads::Threads)
+endif()
+akerr_instrument_for_coverage(akerror_init_failure)
+akerr_instrument_for_sanitizers(akerror_init_failure)
+
 # Each test is one source file in tests/ built into test_<name> and registered
 # as CTest <name>. Tests expected to abort (unhandled error / contract
 # violation) go in AKERR_WILL_FAIL_TESTS; all others must exit 0.
@@ -227,6 +261,7 @@ set(AKERR_TESTS
     err_registry_init_order
     err_status_exception
     err_copy_string
+    err_init_reservation_fatal
     err_library_status_fatal
     err_refcount_double_fail
     err_stacktrace_bounds
@@ -254,13 +289,18 @@ endif()
 set(AKERR_WILL_FAIL_TESTS
     err_trace
     err_improper_closure
+    err_init_reservation_fatal
     err_library_status_fatal
 )
 
 foreach(_test IN LISTS AKERR_TESTS)
     add_executable(test_${_test} tests/${_test}.c)
     target_include_directories(test_${_test} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/tests)
-    target_link_libraries(test_${_test} PRIVATE akerror)
+    if(_test STREQUAL "err_init_reservation_fatal")
+        target_link_libraries(test_${_test} PRIVATE akerror_init_failure)
+    else()
+        target_link_libraries(test_${_test} PRIVATE akerror)
+    endif()
     if(AKERR_THREAD_SAFE)
         target_link_libraries(test_${_test} PRIVATE Threads::Threads)
     endif()
@@ -305,7 +345,14 @@ if(Python3_FOUND)
     # The script configures and drives its own instrumented build tree (under
     # ${CMAKE_BINARY_DIR}/coverage) so this build's binaries and its coverage
     # counters can never be stale or half-instrumented. Reports via gcov.
-    add_custom_target(coverage
+    # Keep the convenient generic name at the top level, but namespace it when
+    # embedded so a parent project can provide its own coverage target.
+    if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+        set(AKERR_COVERAGE_TARGET coverage)
+    else()
+        set(AKERR_COVERAGE_TARGET akerror_coverage)
+    endif()
+    add_custom_target(${AKERR_COVERAGE_TARGET}
         COMMAND ${Python3_EXECUTABLE}
                 ${CMAKE_CURRENT_SOURCE_DIR}/scripts/coverage.py
                 --source-root ${CMAKE_CURRENT_SOURCE_DIR}
@@ -337,7 +384,6 @@ if(Python3_FOUND)
     )
 endif()
 
-set(main_lib_dest "lib/my_library-${MY_LIBRARY_VERSION}")
 install(TARGETS akerror
   EXPORT akerrorTargets
   ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}

UPGRADING.md

@@ -132,6 +132,11 @@ One recursive lock covers both the pool and the registry, so error
 correctness there is worth more than throughput, but a program that raises
 errors in a hot loop will feel it.
 
+Releasing the last reference to a context remains serialized under that same
+pool lock, but it now resets only the handled/status/reported state, the string
+heads, and the stack-trace cursor. It no longer wipes the whole context buffer,
+so release is a fixed handful of stores rather than a tens-of-kilobytes write.
+
 The per-thread last-ditch context is a whole `akerr_ErrorContext` (tens of
 kilobytes) in thread-local storage, allocated per thread on first use of the
 library from that thread.

src/error.c

@@ -88,7 +88,10 @@ typedef struct
 
 static akerr_StatusName akerr_status_names[AKERR_STATUS_NAME_SLOTS];
 static int akerr_status_name_count;
-static akerr_StatusRange akerr_status_ranges[AKERR_MAX_RESERVED_STATUS_RANGES];
+/* C has no portable zero-length arrays. Keep one unused physical slot when a
+ * test build sets the logical capacity to zero to drive init's fatal path. */
+static akerr_StatusRange akerr_status_ranges[
+    AKERR_MAX_RESERVED_STATUS_RANGES > 0 ? AKERR_MAX_RESERVED_STATUS_RANGES : 1];
 static int akerr_status_range_count;
 
 akerr_ErrorContext AKERR_ARRAY_ERROR[AKERR_MAX_ARRAY_ERROR];
@@ -377,10 +380,10 @@ akerr_ErrorContext *akerr_next_error()
 }
 
 /*
- * The wipe returns the slot to the pool, so it and the decrement that triggers
+ * The reset returns the slot to the pool, so it and the decrement that triggers
  * it are one operation under the lock. Otherwise a thread that saw the count
  * reach zero could be handed the slot by akerr_next_error() and start writing
- * its error into it while the releasing thread was still memsetting it.
+ * its error into it while the releasing thread was still resetting it.
  */
 akerr_ErrorContext *akerr_release_error(akerr_ErrorContext *err)
 {
@@ -398,7 +401,13 @@ akerr_ErrorContext *akerr_release_error(akerr_ErrorContext *err)
     }
     if ( err->refcount == 0 ) {
 	oldid = err->arrayid;
-	memset(err, 0x00, sizeof(akerr_ErrorContext));
+	err->handled = false;
+	err->status = 0;
+	err->reported = false;
+	err->message[0] = '\0';
+	err->fname[0] = '\0';
+	err->function[0] = '\0';
+	err->stacktracebuf[0] = '\0';
 	err->stacktracebufptr = (char *)&err->stacktracebuf;
 	err->arrayid = oldid;
 	remaining = NULL;

tests/err_init_reservation_fatal.c

@@ -0,0 +1,20 @@
+#include "akerror.h"
+
+#include <stdio.h>
+
+/*
+ * This executable links to akerror_init_failure, a test-only library target
+ * with no status-range slots. The first reservation in akerr_init() must be
+ * terminal: continuing would leave every library status unowned and make all
+ * subsequent name registrations invalid.
+ *
+ * CTest marks this WILL_FAIL. Reaching the message and returning zero means
+ * initialization swallowed its own reservation failure.
+ */
+int main(void)
+{
+    akerr_init();
+
+    fprintf(stderr, "err_init_reservation_fatal: akerr_init did not terminate\n");
+    return 0;
+}

tests/err_release_clears.c

@@ -1,24 +1,32 @@
 #include "akerror.h"
 #include "err_capture.h"
-#include <string.h>
 
 /*
- * Releasing an error context back to the pool must wipe it, so the next caller
- * that checks it out never sees stale status/message/stacktrace from a previous
- * error. Mutation testing showed the clearing memset in akerr_release_error
- * could be deleted without any test noticing.
+ * Releasing an error context back to the pool must reset the state that affects
+ * the next caller. In particular, a handled error must not make a fresh error
+ * look handled when its slot is recycled.
  */
 
+static int unhandled_calls = 0;
+static int unhandled_status = 0;
+
+static void test_unhandled_handler(akerr_ErrorContext *errctx)
+{
+    unhandled_calls++;
+    unhandled_status = (errctx != NULL) ? errctx->status : 0;
+}
+
 akerr_ErrorContext *boom(void)
 {
     PREPARE_ERROR(e);
-    FAIL_RETURN(e, AKERR_VALUE, "stale dirty message that must not survive");
+    FAIL_RETURN(e, AKERR_VALUE, "first error is handled");
 }
 
 int main(void)
 {
     akerr_capture_install();
     akerr_init();
+    akerr_handler_unhandled_error = &test_unhandled_handler;
 
     /* Raise and fully handle an error; FINISH_NORETURN releases it to the pool. */
     PREPARE_ERROR(e);
@@ -32,13 +40,31 @@ int main(void)
 
     AKERR_CHECK(e == NULL);
 
-    /* The next context handed out is the slot we just released: it must be clean. */
+    /* A fresh error in the recycled slot must not inherit handled=true. */
+    PREPARE_ERROR(fresh);
+    ATTEMPT {
+	CATCH(fresh, boom());
+    } CLEANUP {
+    } PROCESS(fresh) {
+    } FINISH_NORETURN(fresh);
+
+    AKERR_CHECK(unhandled_calls == 1);
+    AKERR_CHECK(unhandled_status == AKERR_VALUE);
+    AKERR_CHECK(fresh == NULL);
+
+    /* The next context handed out is the same slot, with recycle state reset. */
     akerr_ErrorContext *slot = akerr_next_error();
     AKERR_CHECK(slot != NULL);
+    AKERR_CHECK(slot->handled == false);
     AKERR_CHECK(slot->status == 0);
+    AKERR_CHECK(slot->reported == false);
     AKERR_CHECK(slot->message[0] == '\0');
+    AKERR_CHECK(slot->fname[0] == '\0');
+    AKERR_CHECK(slot->function[0] == '\0');
     AKERR_CHECK(slot->stacktracebuf[0] == '\0');
-    AKERR_CHECK(strstr(slot->message, "stale dirty message") == NULL);
+    AKERR_CHECK(slot->stacktracebufptr == (char *)&slot->stacktracebuf);
+    RELEASE_ERROR(slot);
+    AKERR_CHECK(akerr_slots_in_use() == 0);
 
     fprintf(stderr, "err_release_clears ok\n");
     return 0;