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// Copyright 2018 The Abseil Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
// -----------------------------------------------------------------------------
// File: failure_signal_handler.h
// -----------------------------------------------------------------------------
// This file configures the Abseil *failure signal handler* to capture and dump
// useful debugging information (such as a stacktrace) upon program failure.
// To use the failure signal handler, call `absl::InstallFailureSignalHandler()`
// very early in your program, usually in the first few lines of main():
// int main(int argc, char** argv) {
// // Initialize the symbolizer to get a human-readable stack trace
// absl::InitializeSymbolizer(argv[0]);
// absl::FailureSignalHandlerOptions options;
// absl::InstallFailureSignalHandler(options);
// DoSomethingInteresting();
// return 0;
// }
// Any program that raises a fatal signal (such as `SIGSEGV`, `SIGILL`,
// `SIGFPE`, `SIGABRT`, `SIGTERM`, `SIGBUG`, and `SIGTRAP`) will call the
// installed failure signal handler and provide debugging information to stderr.
// Note that you should *not* install the Abseil failure signal handler more
// than once. You may, of course, have another (non-Abseil) failure signal
// handler installed (which would be triggered if Abseil's failure signal
// handler sets `call_previous_handler` to `true`).
namespace absl {
// FailureSignalHandlerOptions
// Struct for holding `absl::InstallFailureSignalHandler()` configuration
// options.
struct FailureSignalHandlerOptions {
// If true, try to symbolize the stacktrace emitted on failure, provided that
// you have initialized a symbolizer for that purpose. (See symbolize.h for
// more information.)
bool symbolize_stacktrace = true;
// If true, try to run signal handlers on an alternate stack (if supported on
// the given platform). An alternate stack is useful for program crashes due
// to a stack overflow; by running on a alternate stack, the signal handler
// may run even when normal stack space has been exausted. The downside of
// using an alternate stack is that extra memory for the alternate stack needs
// to be pre-allocated.
bool use_alternate_stack = true;
// If positive, indicates the number of seconds after which the failure signal
// handler is invoked to abort the program. Setting such an alarm is useful in
// cases where the failure signal handler itself may become hung or
// deadlocked.
int alarm_on_failure_secs = 3;
// If true, call the previously registered signal handler for the signal that
// was received (if one was registered) after the existing signal handler
// runs. This mechanism can be used to chain signal handlers together.
// If false, the signal is raised to the default handler for that signal
// (which normally terminates the program).
// IMPORTANT: If true, the chained fatal signal handlers must not try to
// recover from the fatal signal. Instead, they should terminate the program
// via some mechanism, like raising the default handler for the signal, or by
// calling `_exit()`. Note that the failure signal handler may put parts of
// the Abseil library into a state from which they cannot recover.
bool call_previous_handler = false;
// If non-null, indicates a pointer to a callback function that will be called
// upon failure, with a std::string argument containing failure data. This function
// may be used as a hook to write failure data to a secondary location, such
// as a log file. This function may also be called with null data, as a hint
// to flush any buffered data before the program may be terminated. Consider
// flushing any buffered data in all calls to this function.
// Since this function runs within a signal handler, it should be
// async-signal-safe if possible.
// See
void (*writerfn)(const char*) = nullptr;
// InstallFailureSignalHandler()
// Installs a signal handler for the common failure signals `SIGSEGV`, `SIGILL`,
// `SIGFPE`, `SIGABRT`, `SIGTERM`, `SIGBUG`, and `SIGTRAP` (provided they exist
// on the given platform). The failure signal handler dumps program failure data
// useful for debugging in an unspecified format to stderr. This data may
// include the program counter, a stacktrace, and register information on some
// systems; do not rely on an exact format for the output, as it is subject to
// change.
void InstallFailureSignalHandler(const FailureSignalHandlerOptions& options);
namespace debugging_internal {
const char* FailureSignalToString(int signo);
} // namespace debugging_internal
} // namespace absl