source: tests/collections/string-gc.cfa @ 3c7e3c4

#include <string_res.hfa>

size_t bytesRemaining() {
    return DEBUG_string_bytes_avail_until_gc( DEBUG_string_heap() );
}

size_t heapOffsetStart( string_res & s ) {
    const char * startByte = DEBUG_string_heap_start( DEBUG_string_heap() );
    assert( s.Handle.s >= startByte );
    return s.Handle.s - startByte;
}

void prtStrRep(const char * label, string_res & s) {
    sout | label | "from" | heapOffsetStart(s) | "to" | (heapOffsetStart(s) + size(s));
}
#define PRT_STR_REP(s) prtStrRep( #s, s )

void basicFillCompact() {
    sout | "======================== basicFillCompact";
    string_res xinit = "hello!";
    string_res x = {xinit, COPY_VALUE};
    string_res padder = "----|";
    sout | x;
    for( 3 ) {
        x += padder;
        sout | x;
    }

    // x and padder overlap
    sout | "--A";
    sout | "length of x:" | size(x);
    PRT_STR_REP(padder);
    PRT_STR_REP(x);

    while ( bytesRemaining() + 1 > 5 ) { // until room for "q" but not another "----|" thereafter
        x += padder;
    }

    // x and padder still overlap; now x is huge
    sout | "--B";
    sout | "length of x:" | size(x);
    PRT_STR_REP(padder);
    PRT_STR_REP(x);

    assert( bytesRemaining() >= 1 );
    x = "q";

    // x and padder no longer overlap; baseline xinit
    sout | "--C";
    PRT_STR_REP(xinit);
    PRT_STR_REP(padder);
    PRT_STR_REP(x);

    // want the next edit to straddle the bound
    assert( bytesRemaining() < size(padder) );

    sout | "--D";
    sout | "before append, x = " | x;     // q
    x += padder;                         // trigger compaction
    sout | "after append, x = " | x;      // q----|

    // x and padder moved to the start
    sout | "--E";
    PRT_STR_REP(xinit);
    PRT_STR_REP(padder);
    PRT_STR_REP(x);

    // plenty of room now
    sout | "--F";
    sout | bytesRemaining() | "bytes available before re-fill";

    // fill it again
    string_res z = "zzz";
    while ( bytesRemaining() > 1 ) {
        z += ".";
    }

    sout | bytesRemaining() | "bytes available after re-fill";

    // ensure not affected (shows it's not referencing an invalid location that hadn't been overwritten from the original value yet)
    // black-box criterion that matches earlier "saw it move"
    sout | "--G";
    sout | "after re-fill, x = " | x;      // q----|

    // leave the heap basically empty, for the next test
    z = "";                        // turn used space into gargbage
    string_res whatever = "asdf";  // trigger compaction
    assert( bytesRemaining() > 100 );
}

void fillCompact_withSharedEdits() {
    // do an assignment that causes a collection to happen, while there are edits shared (substrings)

    sout | "======================== fillCompact_withSharedEdits";

    // mostly fill the pad
    string_res z = "zzz";
    while ( bytesRemaining() > 10 ) {
        z += ".";
    }
    z = "";  // leave compaction possible

    // setup
    string_res x = "hello";
    string_res y = { x, SHARE_EDITS, 0, 5 };
    PRT_STR_REP(x);
    PRT_STR_REP(y);
    sout | "-";

    sout | "before reassign, x = " | x;     // hello
    sout | "before reassign, y = " | y;     // hello

    x = "0123456789"; // compact here

    sout | "after reassign, x = " | x;      // 0123456789
    sout | "after reassign, y = " | y;      // 0123456789

    PRT_STR_REP(x);
    PRT_STR_REP(y);
}

void fillNoCompact() {
    // show that allocating in a heap filled with mostly live strings (no collectable garbage) causes heap growth

    sout | "======================== fillNoCompact";

    size_t lastTimeBytesAvail = bytesRemaining();
    assert( lastTimeBytesAvail >= 200 ); // starting this test with nontrivial room

    // mostly fill the pad
    string_res a = "aaa";  // will have to be moved
    string_res z = "zzz";
    for (i; 5) {
        while ( bytesRemaining() > 10 ) {
            z += ".";
        }
        sout | "about to expand, a = " | a;
        while ( bytesRemaining() <= 10 ) {
            z += ".";
        }
        sout | "expanded, a = " | a;

        // each growth gives more usable space than the last
        assert( bytesRemaining() > lastTimeBytesAvail );
        lastTimeBytesAvail = bytesRemaining();
    }
}

int main() {
    basicFillCompact();
    fillCompact_withSharedEdits();
    fillNoCompact();
}