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-= Caveats for implementing Signal.trap callbacks
-
-As with implementing signal handlers in C or most other languages,
-all code passed to Signal.trap must be reentrant.  If you are not
-familiar with reentrancy, you need to read up on it at
-{Wikipedia}[https://en.wikipedia.org/wiki/Reentrancy_(computing)] or
-elsewhere before reading the rest of this document.
-
-Most importantly, "thread-safety" does not guarantee reentrancy;
-and methods such as Mutex#lock and Mutex#synchronize which are
-commonly used for thread-safety even prevent reentrancy.
-
-== An implementation detail of the Ruby VM
-
-The Ruby VM defers Signal.trap callbacks from running until it is safe
-for its internal data structures, but it does not know when it is safe
-for data structures in YOUR code.  Ruby implements deferred signal
-handling by registering short C functions with only
-{async-signal-safe functions}[http://man7.org/linux/man-pages/man7/signal-safety.7.html] as
-signal handlers.  These short C functions only do enough tell the VM to
-run callbacks registered via Signal.trap later in the main Ruby Thread.
-
-== Unsafe methods to call in Signal.trap blocks
-
-When in doubt, consider anything not listed as safe below as being
-unsafe.
-
-* Mutex#lock, Mutex#synchronize and any code using them are explicitly
-  unsafe.  This includes Monitor in the standard library which uses
-  Mutex to provide reentrancy.
-
-* Dir.chdir with block
-
-* any IO write operations when IO#sync is false;
-  including IO#write, IO#write_nonblock, IO#puts.
-  Pipes and sockets default to `IO#sync = true', so it is safe to
-  write to them unless IO#sync was disabled.
-
-* File#flock, as the underlying flock(2) call is not specified by POSIX
-
-== Commonly safe operations inside Signal.trap blocks
-
-* Assignment and retrieval of local, instance, and class variables
-
-* Most object allocations and initializations of common types
-  including Array, Hash, String, Struct, Time.
-
-* Common Array, Hash, String, Struct operations which do not execute a block
-  are generally safe; but beware if iteration is occurring elsewhere.
-
-* Hash#[], Hash#[]= (unless Hash.new was given an unsafe block)
-
-* Thread::Queue#push and Thread::SizedQueue#push (since Ruby 2.1)
-
-* Creating a new Thread via Thread.new/Thread.start can used to get
-  around the unusability of Mutexes inside a signal handler
-
-* Signal.trap is safe to use inside blocks passed to Signal.trap
-
-* arithmetic on Integer and Float (`+', `-', '%', '*', '/')
-
-  Additionally, signal handlers do not run between two successive
-  local variable accesses, so shortcuts such as `+=' and `-=' will
-  not trigger a data race when used on Integer and Float classes in
-  signal handlers.
-
-== System call wrapper methods which are safe inside Signal.trap
-
-Since Ruby has wrappers around many
-{async-signal-safe C functions}[http://man7.org/linux/man-pages/man7/signal-safety.7.html]
-the corresponding wrappers for many IO, File, Dir, and Socket methods
-are safe.
-
-(Incomplete list)
-
-* Dir.chdir (without block arg)
-* Dir.mkdir
-* Dir.open
-* File#truncate
-* File.link
-* File.open
-* File.readlink
-* File.rename
-* File.stat
-* File.symlink
-* File.truncate
-* File.unlink
-* File.utime
-* IO#close
-* IO#dup
-* IO#fsync
-* IO#read
-* IO#read_nonblock
-* IO#stat
-* IO#sysread
-* IO#syswrite
-* IO.select
-* IO.pipe
-* Process.clock_gettime
-* Process.exit!
-* Process.fork
-* Process.kill
-* Process.pid
-* Process.ppid
-* Process.waitpid
-...