error.jl

# This file is a part of Julia. License is MIT: http://julialang.org/license

# pseudo-definitions to show how everything behaves
#
# throw(label, val) = # throw a value to a dynamically enclosing block
#
# function rethrow(val)
#     global current_exception = val
#     throw(current_handler(), current_exception)
# end
#
# rethrow() = rethrow(current_exception)
#
# function throw(val)
#     global catch_backtrace = backtrace()
#     rethrow(val)
# end

## native julia error handling ##

error(s::AbstractString) = throw(ErrorException(s))

"""
    error(msg...)

Raise an `ErrorException` with the given message.

See also [`logging`](@ref).
"""
error(s...) = throw(ErrorException(Main.Base.string(s...)))

"""
    rethrow([e])

Throw an object without changing the current exception backtrace. The default argument is
the current exception (if called within a `catch` block).
"""
rethrow() = ccall(:jl_rethrow, Bottom, ())
rethrow(e) = ccall(:jl_rethrow_other, Bottom, (Any,), e)

"""
    backtrace()

Get a backtrace object for the current program point.
"""
backtrace() = ccall(:jl_backtrace_from_here, Array{Ptr{Void},1}, (Int32,), false)

"""
    catch_backtrace()

Get the backtrace of the current exception, for use within `catch` blocks.
"""
catch_backtrace() = ccall(:jl_get_backtrace, Array{Ptr{Void},1}, ())

## keyword arg lowering generates calls to this ##
kwerr(kw, args...) = throw(MethodError(typeof(args[1]).name.mt.kwsorter, (kw,args...)))

## system error handling ##
"""
    systemerror(sysfunc, iftrue)

Raises a `SystemError` for `errno` with the descriptive string `sysfunc` if `iftrue` is `true`
"""
systemerror(p, b::Bool; extrainfo=nothing) = b ? throw(Main.Base.SystemError(string(p), Libc.errno(), extrainfo)) : nothing

## assertion functions and macros ##

assert(x) = x ? nothing : throw(Main.Base.AssertionError())
macro assert(ex, msgs...)
    msg = isempty(msgs) ? ex : msgs[1]
    if isa(msg, AbstractString)
        msg = msg # pass-through
    elseif !isempty(msgs) && (isa(msg, Expr) || isa(msg, Symbol))
        # message is an expression needing evaluating
        msg = :(Main.Base.string($(esc(msg))))
    elseif isdefined(Main, :Base) && isdefined(Main.Base, :string) && applicable(Main.Base.string, msg)
        msg = Main.Base.string(msg)
    else
        # string() might not be defined during bootstrap
        msg = :(Main.Base.string($(Expr(:quote,msg))))
    end
    return :($(esc(ex)) ? $(nothing) : throw(Main.Base.AssertionError($msg)))
end

struct ExponentialBackOff
    n::Int
    first_delay::Float64
    max_delay::Float64
    factor::Float64
    jitter::Float64

    function ExponentialBackOff(n, first_delay, max_delay, factor, jitter)
        all(x->x>=0, (n, first_delay, max_delay, factor, jitter)) || error("all inputs must be non-negative")
        new(n, first_delay, max_delay, factor, jitter)
    end
end

"""
    ExponentialBackOff(; n=1, first_delay=0.05, max_delay=10.0, factor=5.0, jitter=0.1)

A `Float64` iterator of length `n` whose elements exponentially increase at a
rate in the interval `factor` * (1 ± `jitter`).  The first element is
`first_delay` and all elements are clamped to `max_delay`.
"""
ExponentialBackOff(; n=1, first_delay=0.05, max_delay=10.0, factor=5.0, jitter=0.1) =
    ExponentialBackOff(n, first_delay, max_delay, factor, jitter)
start(ebo::ExponentialBackOff) = (ebo.n, min(ebo.first_delay, ebo.max_delay))
function next(ebo::ExponentialBackOff, state)
    next_n = state[1]-1
    curr_delay = state[2]
    next_delay = min(ebo.max_delay, state[2] * ebo.factor * (1.0 - ebo.jitter + (rand() * 2.0 * ebo.jitter)))
    (curr_delay, (next_n, next_delay))
end
done(ebo::ExponentialBackOff, state) = state[1]<1
length(ebo::ExponentialBackOff) = ebo.n

"""
    retry(f::Function;  delays=ExponentialBackOff(), check=nothing) -> Function

Returns an anonymous function that calls function `f`.  If an exception arises,
`f` is repeatedly called again, each time `check` returns `true`, after waiting the
number of seconds specified in `delays`.  `check` should input `delays`'s
current state and the `Exception`.

# Examples
```julia
retry(f, delays=fill(5.0, 3))
retry(f, delays=rand(5:10, 2))
retry(f, delays=Base.ExponentialBackOff(n=3, first_delay=5, max_delay=1000))
retry(http_get, check=(s,e)->e.status == "503")(url)
retry(read, check=(s,e)->isa(e, UVError))(io)
```
"""
function retry(f::Function;  delays=ExponentialBackOff(), check=nothing)
    (args...) -> begin
        state = start(delays)
        while true
            try
                return f(args...)
            catch e
                done(delays, state) && rethrow(e)
                if check !== nothing
                    state, retry_or_not = check(state, e)
                    retry_or_not || rethrow(e)
                end
            end
            (delay, state) = next(delays, state)
            sleep(delay)
        end
    end
end