内容简介：最近在优化项目，发现字符串拼接的堆内存非常大，而且非常频繁。大概原因如下1.字符串就是char[] 长短发生变化必然要重新分配长度，以及拷贝之前的部分，产生GC
最近在优化项目，发现字符串拼接的堆内存非常大，而且非常频繁。
大概原因如下
1.字符串就是char[] 长短发生变化必然要重新分配长度，以及拷贝之前的部分，产生GC
2.字符串+=进行拼接会产生装箱，生成GC
3.Append传入值类型数据，它会调用ToString方法，需要new string 然后把char[]拷进去，又会产生堆内存。
4.new StringBuidler 产生堆内存
5.StringBuidler.ToString 产生堆内存
5.string.format 它内部使用的就是StringBuilder，但是 1)new StringBuilder 2)Append 3)ToString都会产生堆内存。
所以我们需要优化的是
1.
int a = 100;
string b = a + “”;
禁止上述这种写法，会额外产生一次装箱操作。所以要采用如下写法。
string b = a.ToString();
2.少用或者不用string.format，提前缓存共享StringBuilder对象。避免用时候产生堆内存。
3.网上找到一个算法，挺有意思。提前定义好 0 – 9 之间的字符数组，如果传入值类型数据，从高位依次除以10算出每一位的数，然后再去预先声明的0-9字符数组中找对应的char，这样就就不会产生装箱GC了。
4.如果可以提前确定字符串的长度，例如，界面上显示玩家的等级， 我们可以确定level不可能超过3位数也就是100，那么可以提前声明一个长度为3的StringBuilder，通过反射取出来内部的_str，这样就可以避免最后的ToString产生的堆内存了。由于_str内容可能无法擦掉之前的所以需要调用GarbageFreeClear();方法。
1.装箱版本
using System.Text;
using UnityEngine;
using UnityEngine.Profiling;
public class NewBehaviourScript : MonoBehaviour {
StringBuilder m_StringBuilder = new StringBuilder(100);
string m_StringBuildertxt = string.Empty;
private void Start()
{
m_StringBuildertxt = m_StringBuilder.GetGarbageFreeString();
}
private void Update()
{
int i = Random.Range(0, 100);
float f = Random.Range(0.01f, 200.01f);
float d = Random.Range(0.01f, 200.01f);
string s = "yusong: " + i;
Profiler.BeginSample("string.format");
string s1 = string.Format("{0}{1}{2}{3}", i, f, d, s);
Profiler.EndSample();
Profiler.BeginSample("+=");
string s2 = i +"" + f +"" + d +"" + s;
Profiler.EndSample();
Profiler.BeginSample("StringBuilder");
string s3 = new StringBuilder().Append(i).Append(f).Append(d).Append(s).ToString();
Profiler.EndSample();
Profiler.BeginSample("StrExt.Format");
string s4 = StrExt.Format("{0}{1:0.00}{2:0.00}{3}", i, f, d, s);
Profiler.EndSample();
Profiler.BeginSample("EmptyGC");
m_StringBuilder.GarbageFreeClear();
m_StringBuilder.ConcatFormat("{0}{1:0.00}{2:0.00}{3}", i, f, d, s);
string s5 = m_StringBuildertxt;
Profiler.EndSample();
Debug.LogFormat("s1 : {0}",s1);
Debug.LogFormat("s2 : {0}", s2);
Debug.LogFormat("s3 : {0}", s3);
Debug.LogFormat("s4 : {0}", s4);
Debug.LogFormat("s5 : {0}", s5);
}
}
2.无装箱版本
using System.Text;
using UnityEngine;
using UnityEngine.Profiling;
public class NewBehaviourScript : MonoBehaviour {
StringBuilder m_StringBuilder = new StringBuilder(100);
string m_StringBuildertxt = string.Empty;
private void Start()
{
m_StringBuildertxt = m_StringBuilder.GetGarbageFreeString();
}
private void Update()
{
int i = Random.Range(0, 100);
float f = Random.Range(0.01f, 200.01f);
float d = Random.Range(0.01f, 200.01f);
string s = "yusong: " + i.ToString();
Profiler.BeginSample("string.format");
string s1 = string.Format("{0}{1}{2}{3}", i.ToString(), f.ToString(), d.ToString(), s);
Profiler.EndSample();
Profiler.BeginSample("+=");
string s2 = i.ToString() + f.ToString() + d.ToString() + s;
Profiler.EndSample();
Profiler.BeginSample("StringBuilder");
string s3 = new StringBuilder().Append(i).Append(f).Append(d).Append(s).ToString();
Profiler.EndSample();
Profiler.BeginSample("StrExt.Format");
string s4 = StrExt.Format("{0}{1:0.00}{2:0.00}{3}", i, f, d, s);
Profiler.EndSample();
Profiler.BeginSample("EmptyGC");
m_StringBuilder.GarbageFreeClear();
m_StringBuilder.ConcatFormat("{0}{1:0.00}{2:0.00}{3}", i, f, d, s);
string s5 = m_StringBuildertxt;
Profiler.EndSample();
Debug.LogFormat("s1 : {0}", s1);
Debug.LogFormat("s2 : {0}", s2);
Debug.LogFormat("s3 : {0}", s3);
Debug.LogFormat("s4 : {0}", s4);
Debug.LogFormat("s5 : {0}", s5);
}
}
通通过这两张图大家可以看出来装箱和不装箱对GC有多大的影响了，还有最后的无GC版本。代码参考了下面的这两篇文章。
http://www.gavpugh.com/2010/04/05/xnac-a-garbage-free-stringbuilder-format-method/
http://www.gavpugh.com/2010/03/23/xnac-stringbuilder-to-string-with-no-garbage/using System;
using System.Text;
using UnityEngine;
public static class StringBuilderExtensions
{
// These digits are here in a static array to support hex with simple, easily-understandable code.
// Since A-Z don't sit next to 0-9 in the ascii table.
private static readonly char[] ms_digits = new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
private static readonly uint ms_default_decimal_places = 5; //< Matches standard .NET formatting dp's
private static readonly char ms_default_pad_char = '0';
//! Convert a given unsigned integer value to a string and concatenate onto the stringbuilder. Any base value allowed.
public static StringBuilder Concat(this StringBuilder string_builder, uint uint_val, uint pad_amount, char pad_char, uint base_val)
{
Debug.Assert(pad_amount >= 0);
Debug.Assert(base_val > 0 && base_val <= 16);
// Calculate length of integer when written out
uint length = 0;
uint length_calc = uint_val;
do
{
length_calc /= base_val;
length++;
}
while (length_calc > 0);
// Pad out space for writing.
string_builder.Append(pad_char, (int)Math.Max(pad_amount, length));
int strpos = string_builder.Length;
// We're writing backwards, one character at a time.
while (length > 0)
{
strpos--;
// Lookup from static char array, to cover hex values too
string_builder[strpos] = ms_digits[uint_val % base_val];
uint_val /= base_val;
length--;
}
return string_builder;
}
//! Convert a given unsigned integer value to a string and concatenate onto the stringbuilder. Assume no padding and base ten.
public static StringBuilder Concat(this StringBuilder string_builder, uint uint_val)
{
string_builder.Concat(uint_val, 0, ms_default_pad_char, 10);
return string_builder;
}
//! Convert a given unsigned integer value to a string and concatenate onto the stringbuilder. Assume base ten.
public static StringBuilder Concat(this StringBuilder string_builder, uint uint_val, uint pad_amount)
{
string_builder.Concat(uint_val, pad_amount, ms_default_pad_char, 10);
return string_builder;
}
//! Convert a given unsigned integer value to a string and concatenate onto the stringbuilder. Assume base ten.
public static StringBuilder Concat(this StringBuilder string_builder, uint uint_val, uint pad_amount, char pad_char)
{
string_builder.Concat(uint_val, pad_amount, pad_char, 10);
return string_builder;
}
//! Convert a given signed integer value to a string and concatenate onto the stringbuilder. Any base value allowed.
public static StringBuilder Concat(this StringBuilder string_builder, int int_val, uint pad_amount, char pad_char, uint base_val)
{
Debug.Assert(pad_amount >= 0);
Debug.Assert(base_val > 0 && base_val <= 16);
// Deal with negative numbers
if (int_val < 0)
{
string_builder.Append('-');
uint uint_val = uint.MaxValue - ((uint)int_val) + 1; //< This is to deal with Int32.MinValue
string_builder.Concat(uint_val, pad_amount, pad_char, base_val);
}
else
{
string_builder.Concat((uint)int_val, pad_amount, pad_char, base_val);
}
return string_builder;
}
//! Convert a given signed integer value to a string and concatenate onto the stringbuilder. Assume no padding and base ten.
public static StringBuilder Concat(this StringBuilder string_builder, int int_val)
{
string_builder.Concat(int_val, 0, ms_default_pad_char, 10);
return string_builder;
}
//! Convert a given signed integer value to a string and concatenate onto the stringbuilder. Assume base ten.
public static StringBuilder Concat(this StringBuilder string_builder, int int_val, uint pad_amount)
{
string_builder.Concat(int_val, pad_amount, ms_default_pad_char, 10);
return string_builder;
}
//! Convert a given signed integer value to a string and concatenate onto the stringbuilder. Assume base ten.
public static StringBuilder Concat(this StringBuilder string_builder, int int_val, uint pad_amount, char pad_char)
{
string_builder.Concat(int_val, pad_amount, pad_char, 10);
return string_builder;
}
//! Convert a given float value to a string and concatenate onto the stringbuilder
public static StringBuilder Concat(this StringBuilder string_builder, float float_val, uint decimal_places, uint pad_amount, char pad_char)
{
Debug.Assert(pad_amount >= 0);
if (decimal_places == 0)
{
// No decimal places, just round up and print it as an int
// Agh, Math.Floor() just works on doubles/decimals. Don't want to cast! Let's do this the old-fashioned way.
int int_val;
if (float_val >= 0.0f)
{
// Round up
int_val = (int)(float_val + 0.5f);
}
else
{
// Round down for negative numbers
int_val = (int)(float_val - 0.5f);
}
string_builder.Concat(int_val, pad_amount, pad_char, 10);
}
else
{
int int_part = (int)float_val;
// First part is easy, just cast to an integer
string_builder.Concat(int_part, pad_amount, pad_char, 10);
// Decimal point
string_builder.Append('.');
// Work out remainder we need to print after the d.p.
float remainder = Math.Abs(float_val - int_part);
// Multiply up to become an int that we can print
do
{
remainder *= 10;
decimal_places--;
}
while (decimal_places > 0);
// Round up. It's guaranteed to be a positive number, so no extra work required here.
remainder += 0.5f;
// All done, print that as an int!
string_builder.Concat((uint)remainder, 0, '0', 10);
}
return string_builder;
}
//! Convert a given float value to a string and concatenate onto the stringbuilder. Assumes five decimal places, and no padding.
public static StringBuilder Concat(this StringBuilder string_builder, float float_val)
{
string_builder.Concat(float_val, ms_default_decimal_places, 0, ms_default_pad_char);
return string_builder;
}
//! Convert a given float value to a string and concatenate onto the stringbuilder. Assumes no padding.
public static StringBuilder Concat(this StringBuilder string_builder, float float_val, uint decimal_places)
{
string_builder.Concat(float_val, decimal_places, 0, ms_default_pad_char);
return string_builder;
}
//! Convert a given float value to a string and concatenate onto the stringbuilder.
public static StringBuilder Concat(this StringBuilder string_builder, float float_val, uint decimal_places, uint pad_amount)
{
string_builder.Concat(float_val, decimal_places, pad_amount, ms_default_pad_char);
return string_builder;
}
//! Concatenate a formatted string with arguments
public static StringBuilder ConcatFormat<A>(this StringBuilder string_builder, String format_string, A arg1)
where A : IConvertible
{
return string_builder.ConcatFormat<A, int, int, int>(format_string, arg1, 0, 0, 0);
}
//! Concatenate a formatted string with arguments
public static StringBuilder ConcatFormat<A, B>(this StringBuilder string_builder, String format_string, A arg1, B arg2)
where A : IConvertible
where B : IConvertible
{
return string_builder.ConcatFormat<A, B, int, int>(format_string, arg1, arg2, 0, 0);
}
//! Concatenate a formatted string with arguments
public static StringBuilder ConcatFormat<A, B, C>(this StringBuilder string_builder, String format_string, A arg1, B arg2, C arg3)
where A : IConvertible
where B : IConvertible
where C : IConvertible
{
return string_builder.ConcatFormat<A, B, C, int>(format_string, arg1, arg2, arg3, 0);
}
//! Concatenate a formatted string with arguments
public static StringBuilder ConcatFormat<A, B, C, D>(this StringBuilder string_builder, String format_string, A arg1, B arg2, C arg3, D arg4)
where A : IConvertible
where B : IConvertible
where C : IConvertible
where D : IConvertible
{
int verbatim_range_start = 0;
for (int index = 0; index < format_string.Length; index++)
{
if (format_string[index] == '{')
{
// Formatting bit now, so make sure the last block of the string is written out verbatim.
if (verbatim_range_start < index)
{
// Write out unformatted string portion
string_builder.Append(format_string, verbatim_range_start, index - verbatim_range_start);
}
uint base_value = 10;
uint padding = 0;
uint decimal_places = 5; // Default decimal places in .NET libs
index++;
char format_char = format_string[index];
if (format_char == '{')
{
string_builder.Append('{');
index++;
}
else
{
index++;
if (format_string[index] == ':')
{
// Extra formatting. This is a crude first pass proof-of-concept. It's not meant to cover
// comprehensively what the .NET standard library Format() can do.
index++;
// Deal with padding
while (format_string[index] == '0')
{
index++;
padding++;
}
if (format_string[index] == 'X')
{
index++;
// Print in hex
base_value = 16;
// Specify amount of padding ( "{0:X8}" for example pads hex to eight characters
if ((format_string[index] >= '0') && (format_string[index] <= '9'))
{
padding = (uint)(format_string[index] - '0');
index++;
}
}
else if (format_string[index] == '.')
{
index++;
// Specify number of decimal places
decimal_places = 0;
while (format_string[index] == '0')
{
index++;
decimal_places++;
}
}
}
// Scan through to end bracket
while (format_string[index] != '}')
{
index++;
}
// Have any extended settings now, so just print out the particular argument they wanted
switch (format_char)
{
case '0': string_builder.ConcatFormatValue<A>(arg1, padding, base_value, decimal_places); break;
case '1': string_builder.ConcatFormatValue<B>(arg2, padding, base_value, decimal_places); break;
case '2': string_builder.ConcatFormatValue<C>(arg3, padding, base_value, decimal_places); break;
case '3': string_builder.ConcatFormatValue<D>(arg4, padding, base_value, decimal_places); break;
default: Debug.Assert(false, "Invalid parameter index"); break;
}
}
// Update the verbatim range, start of a new section now
verbatim_range_start = (index + 1);
}
}
// Anything verbatim to write out?
if (verbatim_range_start < format_string.Length)
{
// Write out unformatted string portion
string_builder.Append(format_string, verbatim_range_start, format_string.Length - verbatim_range_start);
}
return string_builder;
}
//! The worker method. This does a garbage-free conversion of a generic type, and uses the garbage-free Concat() to add to the stringbuilder
private static void ConcatFormatValue<T>(this StringBuilder string_builder, T arg, uint padding, uint base_value, uint decimal_places) where T : IConvertible
{
switch (arg.GetTypeCode())
{
case System.TypeCode.UInt32:
{
string_builder.Concat(arg.ToUInt32(System.Globalization.NumberFormatInfo.CurrentInfo), padding, '0', base_value);
break;
}
case System.TypeCode.Int32:
{
string_builder.Concat(arg.ToInt32(System.Globalization.NumberFormatInfo.CurrentInfo), padding, '0', base_value);
break;
}
case System.TypeCode.Single:
{
string_builder.Concat(arg.ToSingle(System.Globalization.NumberFormatInfo.CurrentInfo), decimal_places, padding, '0');
break;
}
case System.TypeCode.String:
{
string_builder.Append(Convert.ToString(arg));
break;
}
default:
{
Debug.Assert(false, "Unknown parameter type");
break;
}
}
}
public static void Empty(this StringBuilder string_builder)
{
string_builder.Remove(0, string_builder.Length);
}
public static string GetGarbageFreeString(this StringBuilder string_builder)
{
return (string)string_builder.GetType().GetField("_str", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance).GetValue(string_builder);
}
public static void GarbageFreeClear(this StringBuilder string_builder)
{
string_builder.Length = 0;
string_builder.Append(' ', string_builder.Capacity);
string_builder.Length = 0;
}
}
public static class StrExt
{
//只允许拼接50个字符串
private static StringBuilder s_StringBuilder = new StringBuilder(50, 50);
public static string Format<A>(String format_string, A arg1)
where A : IConvertible
{
s_StringBuilder.Empty();
return s_StringBuilder.ConcatFormat<A, int, int, int>(format_string, arg1, 0, 0, 0).ToString();
}
public static string Format<A, B>(String format_string, A arg1, B arg2)
where A : IConvertible
where B : IConvertible
{
s_StringBuilder.Empty();
return s_StringBuilder.ConcatFormat<A, B, int, int>(format_string, arg1, arg2, 0, 0).ToString();
}
public static string Format<A, B, C>(String format_string, A arg1, B arg2, C arg3)
where A : IConvertible
where B : IConvertible
where C : IConvertible
{
s_StringBuilder.Empty();
return s_StringBuilder.ConcatFormat<A, B, C, int>(format_string, arg1, arg2, arg3, 0).ToString();
}
public static string Format<A, B, C, D>(String format_string, A arg1, B arg2, C arg3, D arg4)
where A : IConvertible
where B : IConvertible
where C : IConvertible
where D : IConvertible
{
s_StringBuilder.Empty();
return s_StringBuilder.ConcatFormat<A, B, C, D>(format_string, arg1, arg2, arg3, arg4).ToString();
}
}
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