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Added a new utility class that I have wanted for a while. The CleanUp 

class is a templatized class that allows you to have a cleanup function called
on a data value of type T when the value is set or when the object goes
out of scope. It has support for very rudimentary invalid value detection that
can be enabled by using the appropriate constructor. 

Anyone with template experience that can see ways of improving this class
please let me know. The example code shows a few typical scenarios in which
I would like to use it. It is currently coded with simple type T values
in mind (integer file descriptors, pointers, etc), but I am sure some 
specialization might help out the class for more complex types.

There is a lot of documentation including examples in the CleanUp.h header 
file. 

llvm-svn: 109239
This commit is contained in:
Greg Clayton 2010-07-23 17:42:15 +00:00
parent 896dff661a
commit aaa58c6679
2 changed files with 192 additions and 0 deletions
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188
lldb/include/lldb/Utility/CleanUp.h Normal file
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@ -0,0 +1,188 @@
//===-- CleanUp.h -----------------------------------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#ifndef liblldb_CleanUp_h_
#define liblldb_CleanUp_h_
#include "lldb/lldb-include.h"
namespace lldb_utility {
//----------------------------------------------------------------------
// Templated class that guarantees that a cleanup callback function will
// be called. The cleanup function will be called once under the
// following conditions:
// - when the object goes out of scope
// - when the user explicitly calls clean.
// - the current value will be cleaned up when a new value is set using
// set(T value) as long as the current value hasn't already been cleaned.
//
// This class is designed to be used with simple types for type T (like
// file descriptors, opaque handles, pointers, etc). If more complex
// type T objects are desired, we need to probably specialize this class
// to take "const T&" for all input T parameters. Yet if a type T is
// complex already it might be better to build the cleanup funcionality
// into T.
//
// The cleanup function must take one argument that is of type T.
// The calback fucntion return type is R. The return value is currently
// needed for "CallbackType". If there is an easy way to get around the
// need for the return value we can change this class.
//
// The two template parameters are:
// T - The variable type of value that will be stored and used as the
// sole argument for the cleanup callback.
// R - The return type for the cleanup function.
//
// EXAMPLES
// // Use with file handles that get opened where you want to close
// // them. Below we use "int open(const char *path, int oflag, ...)"
// // which returns an integer file descriptor. -1 is the invalid file
// // descriptor so to make an object that will call "int close(int fd)"
// // automatically we can use:
//
// CleanUp <int, int> fd(open("/tmp/a.txt", O_RDONLY, 0), -1, close);
//
// // malloc/free example
// CleanUp <void *, void> malloced_bytes(malloc(32), NULL, free);
//----------------------------------------------------------------------
template <typename T, typename R>
class CleanUp
{
public:
typedef T value_type;
typedef R (*CallbackType)(value_type);
//----------------------------------------------------------------------
// Constructor that sets the current value only. No values are
// considered to be invalid and the cleanup function will be called
// regardless of the value of m_current_value.
//----------------------------------------------------------------------
CleanUp (value_type value, CallbackType callback) :
m_current_value (value),
m_invalid_value (),
m_callback (callback),
m_callback_called (false),
m_invalid_value_is_valid (false)
{
}
//----------------------------------------------------------------------
// Constructor that sets the current value and also the invalid value.
// The cleanup function will be called on "m_value" as long as it isn't
// equal to "m_invalid_value".
//----------------------------------------------------------------------
CleanUp (value_type value, value_type invalid, CallbackType callback) :
m_current_value (value),
m_callback (callback),
m_invalid_value (invalid),
m_callback_called (false),
m_invalid_value_is_valid (true)
{
}
//----------------------------------------------------------------------
// Automatically cleanup when this object goes out of scope.
//----------------------------------------------------------------------
~CleanUp ()
{
clean();
}
//----------------------------------------------------------------------
// Access the value stored in this class
//----------------------------------------------------------------------
value_type get()
{
return m_current_value;
}
//----------------------------------------------------------------------
// Access the value stored in this class
//----------------------------------------------------------------------
const value_type
get() const
{
return m_current_value;
}
//----------------------------------------------------------------------
// Reset the owned value to "value". If a current value is valid and
// the cleanup callback hasn't been called, the previous value will
// be cleaned up (see void CleanUp::clean()).
//----------------------------------------------------------------------
void
set (const value_type value)
{
// Cleanup the current value if needed
clean ();
// Now set the new value and mark our callback as not called
m_callback_called = false;
m_current_value = value;
}
//----------------------------------------------------------------------
// Checks is "m_current_value" is valid. The value is considered valid
// no invalid value was supplied during construction of this object or
// if an invalid value was supplied and "m_current_value" is not equal
// to "m_invalid_value".
//
// Returns true if "m_current_value" is valid, false otherwise.
//----------------------------------------------------------------------
bool
is_valid() const
{
if (m_invalid_value_is_valid)
return m_current_value != m_invalid_value;
return true;
}
//----------------------------------------------------------------------
// This function will call the cleanup callback provided in the
// constructor one time if the value is considered valid (See is_valid()).
// This function sets m_callback_called to true so we don't call the
// cleanup callback multiple times on the same value.
//----------------------------------------------------------------------
void
clean()
{
if (m_callback && !m_callback_called)
{
m_callback_called = true;
if (is_valid())
m_callback(m_current_value);
}
}
//----------------------------------------------------------------------
// Cancels the cleanup that would have been called on "m_current_value"
// if it was valid. This function can be used to release the value
// contained in this object so ownership can be transfered to the caller.
//----------------------------------------------------------------------
value_type
release ()
{
m_callback_called = true;
return m_current_value;
}
private:
value_type m_current_value;
const value_type m_invalid_value;
CallbackType m_callback;
bool m_callback_called;
bool m_invalid_value_is_valid;
// Outlaw default constructor, copy constructor and the assignment operator
DISALLOW_COPY_AND_ASSIGN (CleanUp);
};
} // namespace lldb_utility
#endif // #ifndef liblldb_CleanUp_h_

4
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