One of Ruby's key features is its exception handling mechanism, which allows developers to handle errors and exceptions in a clean and organized manner. However, using exceptions for error handling can have a negative impact on the performance of a Ruby application, especially if they are used excessively or inappropriately. In this article, we will examine the performance implications of using exceptions in Ruby and discuss some best practices for minimizing their impact on your application's performance.
How exceptions work in Ruby
In Ruby, exceptions are objects that represent an error or exceptional condition that occurs during the execution of a program. When an exception is raised, it is propagated up the call stack until it is caught and handled by an appropriate exception handler. If no exception handler is found, the program will terminate with an unhandled exception error.
Exceptions are raised using the raise keyword, which takes an optional message argument and an optional exception class argument. For example, the following code raises a RuntimeError with the message "Something went wrong":
raise "Something went wrong"
You can also raise a specific exception class, such as ArgumentError:
raise ArgumentError, "Invalid argument"
To handle exceptions, you can use the begin-rescue-end block, which allows you to specify a block of code that may raise an exception and a block of code that will handle the exception if it is raised. For example:
begin # code that may raise an exception rescue # code to handle the exception end
You can also specify a specific exception class or multiple exception classes to rescue:
begin # code that may raise an exception rescue StandardError # code to handle StandardError and its subclasses rescue ArgumentError # code to handle ArgumentError and its subclasses end
Finally, you can use the ensure keyword to specify a block of code that will always be executed, regardless of whether an exception is raised or not:
begin # code that may raise an exception rescue # code to handle the exception ensure # code that will always be executed end
Performance implications of exceptions
Using exceptions for error handling can have a significant impact on the performance of a Ruby application, especially if they are used excessively or inappropriately. This is because raising and handling exceptions involves a significant amount of overhead, including creating and manipulating exception objects, unwinding the call stack, and executing exception handling code.
Here are some ways in which the use of exceptions can affect the performance of a Ruby application:
Object creation overhead: Every time an exception is raised, a new exception object is created and initialized with the appropriate message and exception class. This involves allocating memory and initializing the object, which can be expensive, especially if the exception is raised frequently.
Unwinding the call stack: When an exception is raised, the interpreter must unwind the call stack to find the appropriate exception handler. This involves traversing the call stack and checking each frame for an exception handler, which can be time-consuming and add significant overhead to the program.
Exception handling code: The code in the rescue block is executed every time an exception is raised and handled, which can add additional overhead to the program. If the exception handling code is complex or performs a lot of computations, it can further degrade the performance of the application.
Increased memory usage: Exceptions use more memory than traditional error handling mechanisms, such as returning error codes or using nil values to indicate an error. This is because exception objects are created and stored on the call stack, which can lead to increased memory usage and slower garbage collection.
Slower code execution: The overhead associated with raising and handling exceptions can slow down the overall execution of the program. This is especially noticeable in tight loops or in code that is called frequently.
To minimize the performance impact of exceptions in your Ruby application, it is important to use them appropriately and only when necessary. Here are some best practices for using exceptions in Ruby:
Use exceptions for exceptional situations: Exceptions should be used to handle truly exceptional situations, such as unexpected input, system failures, or other conditions that cannot be handled in a normal way. Do not use exceptions for control flow or as a substitute for traditional error handling mechanisms.
Avoid raising and handling exceptions in tight loops: Avoid raising and handling exceptions in tight loops or in code that is called frequently. This can significantly degrade the performance of the application.
Use specific exception classes: Use specific exception classes, rather than the generic StandardError class, to clearly communicate the nature of the error and make it easier to handle.
Avoid rescuing Exception: Do not rescue the Exception class, as this will catch all exceptions, including those that should not be handled, such as Interrupt and SystemExit. Instead, rescue specific exception classes or use a more general class, such as StandardError, which does not catch system-level exceptions.
Consider using other error handling mechanisms: In some cases, it may be more appropriate to use other error handling mechanisms, such as returning error codes or using nil values to indicate an error. This can be more efficient than using exceptions, especially in cases where the error handling code is called frequently or the overhead of raising and handling exceptions is significant.
Here is a simple benchmark example that compares the performance of using exceptions versus traditional error handling mechanisms in Ruby:
require "benchmark" # Traditional error handling using return codes def divide_using_return_codes(x, y) return nil if y == 0 x / y end # Exception-based error handling def divide_using_exceptions(x, y) raise ZeroDivisionError if y == 0 x / y rescue ZeroDivisionError nil end # Benchmark the two methods n = 1_000_000 Benchmark.bm do |bm| bm.report("return codes") do n.times do divide_using_return_codes(1, 0) end end bm.report("exceptions") do n.times do divide_using_exceptions(1, 0) end end end
user system total real return codes 0.044149 0.000053 0.044202 ( 0.044223) exceptions 0.508261 0.011618 0.519879 ( 0.520129) => [#<Benchmark::Tms:0x000000014106b598 @cstime=0.0, @cutime=0.0, @label="return codes", @real=0.04422300006262958, @stime=5.2999999999997494e-05, @total=0.04420199999999999, @utime=0.044148999999999994>, #<Benchmark::Tms:0x000000015486d8f0 @cstime=0.0, @cutime=0.0, @label="exceptions", @real=0.5201290000695735, @stime=0.011618000000000003, @total=0.5198790000000001, @utime=0.5082610000000001>]
Apple Mac Book Pro 13-inch, M1, 2020 16GB RAM
The output of the benchmark will show the elapsed time for each method, allowing you to compare the performance of the two approaches. You can also modify the benchmark to test different scenarios, such as handling different types of errors or handling errors in tight loops.
Keep in mind that the performance implications of using exceptions will vary depending on the specific use case and the complexity of the error handling code. It is always a good idea to benchmark and profile your code to determine the most appropriate error handling mechanism for your specific needs.
Exceptions are a powerful and useful tool for handling errors and exceptional situations in Ruby. However, it is important to use them appropriately to avoid degrading the performance of your application. By following best practices and using exceptions only when necessary, you can ensure that your application runs smoothly and efficiently.
Top comments (9)
Really informative article! thank you! I ran it on my machine and saw a big difference:
With the other runs also returning more or less the same result
Hi Davide, very interesting!
I noticed that
divide_using_exceptionsmethod has a redundant line that can be removed, since
x / yalready raises
y == 0:
But the surprising part about that is that it performs way worse than the original
divide_using_exceptions_without_first_lineis 20% slower than
divide_using_exceptionseven with a line less! Pretty counterintuitive to me, I'd expect it to perform the same as
divide_using_exceptions, or even slightly faster O.o
thanks Maurizio for your contribution! Very interesting!
"Use exception for exceptional situations" is a good one. Especially when deciding what to use in such exceptional situation is not your responsibility (example: a database driver should not decide what to do if the database in unreachable). Because of that, in general, exceptions belong rather in library code than in application code.
Small nitpick to the blog post though:
raise "some string"will raise
Very informative. I think we should really be avoiding exception handling in tight loops, since in that case the run time might increase considerably
yes I agree!
I'm curious, does it slow down only when
raiseis used or is it the same if I return an object of an Error class
When talking about "raise" in ruby, should mention also its' cousin "throw".