add scopebuffer

mak/MANIFEST

@@ -35,6 +35,7 @@ MANIFEST=\
 	\
 	src\core\internal\hash.d \
 	src\core\internal\convert.d \
+	src\core\internal\scopebuffer.d \
 	\
 	src\core\stdc\complex.d \
 	src\core\stdc\config.d \

src/core/internal/scopebuffer.d

@@ -0,0 +1,382 @@
+
+/*
+ * Copyright: 2014 by Digital Mars
+ * License: $(LINK2 http://boost.org/LICENSE_1_0.txt, Boost License 1.0).
+ * Authors: Walter Bright
+ * Source: $(DRUNTIMESRC core/internal/_scopebuffer.d)
+ */
+
+module core.internal.scopebuffer;
+
+
+//debug=ScopeBuffer;
+
+private import core.exception;
+private import core.stdc.stdlib : realloc;
+
+/**************************************
+ * 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 core.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 core.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.
+ */
+
+@system
+struct ScopeBuffer(T, alias realloc = core.stdc.stdlib.realloc)
+        /+if (isAssignable!T &&
+              !hasElaborateDestructor!T &&
+              !hasElaborateCopyConstructor!T &&
+              !hasElaborateAssign!T)+/
+{
+    import core.stdc.string : memcpy;
+
+    /**************************
+     * 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;
+    }
+
+    unittest
+    {
+        ubyte[10] tmpbuf = void;
+        auto sbuf = ScopeBuffer!ubyte(tmpbuf);
+    }
+
+    /**************************
+     * 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;
+    }
+
+    /****************************
+     * Copying of ScopeBuffer is not allowed.
+     */
+    //@disable this(this);
+
+    /************************
+     * 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;
+    }
+
+    /************************
+     * 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;
+    }
+
+    /******
+     * 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];
+    }
+
+    /// ditto
+    @system T[] opSlice()
+    {
+        assert(used <= bufLen);
+        return buf[0 .. used];
+    }
+
+    /*******
+     * Returns:
+     *  the element at index i.
+     */
+    ref T opIndex(size_t i)
+    {
+        assert(i < bufLen);
+        return buf[i];
+    }
+
+    /***
+     * Returns:
+     *  the number of elements in the ScopeBuffer
+     */
+    @property size_t length() const
+    {
+        return used;
+    }
+
+    /***
+     * 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;
+    }
+
+    alias opDollar = length;
+
+  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;
+
+    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;
+
+        /* 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; }
+    }
+}
+
+unittest
+{
+    import core.stdc.stdio;
+    import std.range;
+
+    char[2] tmpbuf = void;
+    {
+    // Exercise all the lines of code except for assert(0)'s
+    auto textbuf = ScopeBuffer!char(tmpbuf);
+    scope(exit) textbuf.free();
+
+    static assert(isOutputRange!(ScopeBuffer!char, char));
+
+    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');
+
+    textbuf.length = textbuf.length - 1;
+    assert(textbuf[0..textbuf.length] == "axab");
+
+    textbuf.length = 3;
+    assert(textbuf[0..textbuf.length] == "axa");
+    assert(textbuf[textbuf.length - 1] == 'a');
+    assert(textbuf[1..3] == "xa");
+
+    textbuf.put(cast(dchar)'z');
+    assert(textbuf[] == "axaz");
+
+    textbuf.length = 0;                 // reset for reuse
+    assert(textbuf.length == 0);
+
+    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
+
+}
+
+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;
+    }
+
+    auto s = cat("hello", "betty");
+    assert(s == "hellobettyeven more");
+}
+
+/*********************************
+ * 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();
+---
+ */
+
+auto scopeBuffer(T)(T[] tmpbuf)
+{
+    return ScopeBuffer!T(tmpbuf);
+}
+
+unittest
+{
+    ubyte[10] tmpbuf = void;
+    auto sb = scopeBuffer(tmpbuf);
+    scope(exit) sb.free();
+}
+
+unittest
+{
+    ScopeBuffer!(int*) b;
+    int*[] s;
+    b.put(s);
+}