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/* | ||
* Copyright: 2014 by Digital Mars | ||
* License: $(LINK2 http://boost.org/LICENSE_1_0.txt, Boost License 1.0). | ||
* Authors: Walter Bright | ||
* Source: $(PHOBOSSRC std/internal/_scopebuffer.d) | ||
*/ | ||
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module std.internal.scopebuffer; | ||
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//debug=ScopeBuffer; | ||
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private import core.exception; | ||
private import core.stdc.stdlib : realloc; | ||
private import std.traits; | ||
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/************************************** | ||
* ScopeBuffer encapsulates using a local array as a temporary buffer. | ||
* It is initialized with the local array that should be large enough for | ||
* most uses. If the need exceeds the size, ScopeBuffer will resize it | ||
* using malloc() and friends. | ||
* | ||
* ScopeBuffer cannot contain more than (uint.max-16)/2 elements. | ||
* | ||
* ScopeBuffer is an OutputRange. | ||
* | ||
* Since ScopeBuffer potentially stores elements of type T in malloc'd memory, | ||
* those elements are not scanned when the GC collects. This can cause | ||
* memory corruption. Do not use ScopeBuffer when elements of type T point | ||
* to the GC heap. | ||
* | ||
* Example: | ||
--- | ||
import core.stdc.stdio; | ||
import std.internal.scopebuffer; | ||
void main() | ||
{ | ||
char[2] buf = void; | ||
auto textbuf = ScopeBuffer!char(buf); | ||
scope(exit) textbuf.free(); // necessary for cleanup | ||
// Put characters and strings into textbuf, verify they got there | ||
textbuf.put('a'); | ||
textbuf.put('x'); | ||
textbuf.put("abc"); | ||
assert(textbuf.length == 5); | ||
assert(textbuf[1..3] == "xa"); | ||
assert(textbuf[3] == 'b'); | ||
// Can shrink it | ||
textbuf.length = 3; | ||
assert(textbuf[0..textbuf.length] == "axa"); | ||
assert(textbuf[textbuf.length - 1] == 'a'); | ||
assert(textbuf[1..3] == "xa"); | ||
textbuf.put('z'); | ||
assert(textbuf[] == "axaz"); | ||
// Can shrink it to 0 size, and reuse same memory | ||
textbuf.length = 0; | ||
} | ||
--- | ||
* It is invalid to access ScopeBuffer's contents when ScopeBuffer goes out of scope. | ||
* Hence, copying the contents are necessary to keep them around: | ||
--- | ||
import std.internal.scopebuffer; | ||
string cat(string s1, string s2) | ||
{ | ||
char[10] tmpbuf = void; | ||
auto textbuf = ScopeBuffer!char(tmpbuf); | ||
scope(exit) textbuf.free(); | ||
textbuf.put(s1); | ||
textbuf.put(s2); | ||
textbuf.put("even more"); | ||
return textbuf[].idup; | ||
} | ||
--- | ||
* ScopeBuffer is intended for high performance usages in $(D @system) and $(D @trusted) code. | ||
* It is designed to fit into two 64 bit registers, again for high performance use. | ||
* If used incorrectly, memory leaks and corruption can result. Be sure to use | ||
* $(D scope(exit) textbuf.free();) for proper cleanup, and do not refer to a ScopeBuffer | ||
* instance's contents after $(D ScopeBuffer.free()) has been called. | ||
* | ||
* The realloc parameter defaults to C's realloc(). Another can be supplied to override it. | ||
* | ||
* ScopeBuffer instances may be copied, as in: | ||
--- | ||
textbuf = doSomething(textbuf, args); | ||
--- | ||
* which can be very efficent, but these must be regarded as a move rather than a copy. | ||
* Additionally, the code between passing and returning the instance must not throw | ||
* exceptions, otherwise when ScopeBuffer.free() is called, memory may get corrupted. | ||
*/ | ||
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@system | ||
struct ScopeBuffer(T, alias realloc = core.stdc.stdlib.realloc) | ||
if (isAssignable!T && | ||
!hasElaborateDestructor!T && | ||
!hasElaborateCopyConstructor!T && | ||
!hasElaborateAssign!T) | ||
{ | ||
import core.stdc.string : memcpy; | ||
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/************************** | ||
* Initialize with buf to use as scratch buffer space. | ||
* Params: | ||
* buf = Scratch buffer space, must have length that is even | ||
* Example: | ||
* --- | ||
* ubyte[10] tmpbuf = void; | ||
* auto sbuf = ScopeBuffer!ubyte(tmpbuf); | ||
* --- | ||
* If buf was created by the same realloc passed as a parameter | ||
* to ScopeBuffer, then the contents of ScopeBuffer can be extracted without needing | ||
* to copy them, and ScopeBuffer.free() will not need to be called. | ||
*/ | ||
this(T[] buf) | ||
in | ||
{ | ||
assert(!(buf.length & wasResized)); // assure even length of scratch buffer space | ||
assert(buf.length <= uint.max); // because we cast to uint later | ||
} | ||
body | ||
{ | ||
this.buf = buf.ptr; | ||
this.bufLen = cast(uint)buf.length; | ||
} | ||
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unittest | ||
{ | ||
ubyte[10] tmpbuf = void; | ||
auto sbuf = ScopeBuffer!ubyte(tmpbuf); | ||
} | ||
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/************************** | ||
* Releases any memory used. | ||
* This will invalidate any references returned by the [] operator. | ||
* A destructor is not used, because that would make it not POD | ||
* (Plain Old Data) and it could not be placed in registers. | ||
*/ | ||
void free() | ||
{ | ||
debug(ScopeBuffer) buf[0 .. bufLen] = 0; | ||
if (bufLen & wasResized) | ||
realloc(buf, 0); | ||
buf = null; | ||
bufLen = 0; | ||
used = 0; | ||
} | ||
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/**************************** | ||
* Copying of ScopeBuffer is not allowed. | ||
*/ | ||
//@disable this(this); | ||
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/************************ | ||
* Append element c to the buffer. | ||
* This member function makes ScopeBuffer an OutputRange. | ||
*/ | ||
void put(T c) | ||
{ | ||
/* j will get enregistered, while used will not because resize() may change used | ||
*/ | ||
const j = used; | ||
if (j == bufLen) | ||
{ | ||
assert(j <= (uint.max - 16) / 2); | ||
resize(j * 2 + 16); | ||
} | ||
buf[j] = c; | ||
used = j + 1; | ||
} | ||
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/************************ | ||
* Append array s to the buffer. | ||
*/ | ||
void put(const(T)[] s) | ||
{ | ||
const newlen = used + s.length; | ||
assert((cast(ulong)used + s.length) <= uint.max); | ||
const len = bufLen; | ||
if (newlen > len) | ||
{ | ||
assert(len <= uint.max / 2); | ||
resize(newlen <= len * 2 ? len * 2 : newlen); | ||
} | ||
buf[used .. newlen] = cast(T[])s[]; | ||
used = cast(uint)newlen; | ||
} | ||
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/****** | ||
* Retrieve a slice into the result. | ||
* Returns: | ||
* A slice into the temporary buffer that is only | ||
* valid until the next put() or ScopeBuffer goes out of scope. | ||
*/ | ||
@system T[] opSlice(size_t lower, size_t upper) | ||
in | ||
{ | ||
assert(lower <= bufLen); | ||
assert(upper <= bufLen); | ||
assert(lower <= upper); | ||
} | ||
body | ||
{ | ||
return buf[lower .. upper]; | ||
} | ||
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/// ditto | ||
@system T[] opSlice() | ||
{ | ||
assert(used <= bufLen); | ||
return buf[0 .. used]; | ||
} | ||
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/******* | ||
* Returns: | ||
* the element at index i. | ||
*/ | ||
ref T opIndex(size_t i) | ||
{ | ||
assert(i < bufLen); | ||
return buf[i]; | ||
} | ||
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/*** | ||
* Returns: | ||
* the number of elements in the ScopeBuffer | ||
*/ | ||
@property size_t length() const | ||
{ | ||
return used; | ||
} | ||
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/*** | ||
* Used to shrink the length of the buffer, | ||
* typically to 0 so the buffer can be reused. | ||
* Cannot be used to extend the length of the buffer. | ||
*/ | ||
@property void length(size_t i) | ||
in | ||
{ | ||
assert(i <= this.used); | ||
} | ||
body | ||
{ | ||
this.used = cast(uint)i; | ||
} | ||
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alias opDollar = length; | ||
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private: | ||
T* buf; | ||
// Using uint instead of size_t so the struct fits in 2 registers in 64 bit code | ||
uint bufLen; | ||
enum wasResized = 1; // this bit is set in bufLen if we control the memory | ||
uint used; | ||
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void resize(size_t newsize) | ||
in | ||
{ | ||
assert(newsize <= uint.max); | ||
} | ||
body | ||
{ | ||
//writefln("%s: oldsize %s newsize %s", id, buf.length, newsize); | ||
newsize |= wasResized; | ||
void *newBuf = realloc((bufLen & wasResized) ? buf : null, newsize * T.sizeof); | ||
if (!newBuf) | ||
core.exception.onOutOfMemoryError(); | ||
if (!(bufLen & wasResized)) | ||
{ | ||
memcpy(newBuf, buf, used * T.sizeof); | ||
debug(ScopeBuffer) buf[0 .. bufLen] = 0; | ||
} | ||
buf = cast(T*)newBuf; | ||
bufLen = cast(uint)newsize; | ||
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/* This function is called only rarely, | ||
* inlining results in poorer register allocation. | ||
*/ | ||
version (DigitalMars) | ||
/* With dmd, a fake loop will prevent inlining. | ||
* Using a hack until a language enhancement is implemented. | ||
*/ | ||
while (1) { break; } | ||
} | ||
} | ||
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unittest | ||
{ | ||
import core.stdc.stdio; | ||
import std.range; | ||
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char[2] tmpbuf = void; | ||
{ | ||
// Exercise all the lines of code except for assert(0)'s | ||
auto textbuf = ScopeBuffer!char(tmpbuf); | ||
scope(exit) textbuf.free(); | ||
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static assert(isOutputRange!(ScopeBuffer!char, char)); | ||
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textbuf.put('a'); | ||
textbuf.put('x'); | ||
textbuf.put("abc"); // tickle put([])'s resize | ||
assert(textbuf.length == 5); | ||
assert(textbuf[1..3] == "xa"); | ||
assert(textbuf[3] == 'b'); | ||
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textbuf.length = textbuf.length - 1; | ||
assert(textbuf[0..textbuf.length] == "axab"); | ||
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textbuf.length = 3; | ||
assert(textbuf[0..textbuf.length] == "axa"); | ||
assert(textbuf[textbuf.length - 1] == 'a'); | ||
assert(textbuf[1..3] == "xa"); | ||
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textbuf.put(cast(dchar)'z'); | ||
assert(textbuf[] == "axaz"); | ||
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textbuf.length = 0; // reset for reuse | ||
assert(textbuf.length == 0); | ||
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foreach (char c; "asdf;lasdlfaklsdjfalksdjfa;lksdjflkajsfdasdfkja;sdlfj") | ||
{ | ||
textbuf.put(c); // tickle put(c)'s resize | ||
} | ||
assert(textbuf[] == "asdf;lasdlfaklsdjfalksdjfa;lksdjflkajsfdasdfkja;sdlfj"); | ||
} // run destructor on textbuf here | ||
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} | ||
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unittest | ||
{ | ||
string cat(string s1, string s2) | ||
{ | ||
char[10] tmpbuf = void; | ||
auto textbuf = ScopeBuffer!char(tmpbuf); | ||
scope(exit) textbuf.free(); | ||
textbuf.put(s1); | ||
textbuf.put(s2); | ||
textbuf.put("even more"); | ||
return textbuf[].idup; | ||
} | ||
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auto s = cat("hello", "betty"); | ||
assert(s == "hellobettyeven more"); | ||
} | ||
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/********************************* | ||
* This is a slightly simpler way to create a ScopeBuffer instance | ||
* that uses type deduction. | ||
* Params: | ||
* tmpbuf = the initial buffer to use | ||
* Returns: | ||
* an instance of ScopeBuffer | ||
* Example: | ||
--- | ||
ubyte[10] tmpbuf = void; | ||
auto sb = scopeBuffer(tmpbuf); | ||
scope(exit) sp.free(); | ||
--- | ||
*/ | ||
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auto scopeBuffer(T)(T[] tmpbuf) | ||
{ | ||
return ScopeBuffer!T(tmpbuf); | ||
} | ||
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unittest | ||
{ | ||
ubyte[10] tmpbuf = void; | ||
auto sb = scopeBuffer(tmpbuf); | ||
scope(exit) sb.free(); | ||
} | ||
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unittest | ||
{ | ||
ScopeBuffer!(int*) b; | ||
int*[] s; | ||
b.put(s); | ||
} |
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