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Support for non-seastar managed strings #833

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Support for non-seastar managed strings #833

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44 changes: 36 additions & 8 deletions include/seastar/core/sstring.hh
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Original file line number Diff line number Diff line change
Expand Up @@ -65,6 +65,7 @@ class basic_sstring {
struct external_type {
char_type* str;
Size size;
bool is_ref;//all non-managed non-copy string references should set this flag to true
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@nyh nyh Dec 10, 2020 •
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Regardless of whether this patch is needed at all (see my other comment) please note you shouldn't just add something to "external type" - it will make it longer, and longer than "internal_type", and waste space. What you can do is to replace the old "pad" with a single-byte flag. HOWEVER, this byte - in internal - is already used to for the internal size. So maybe you should pick a specific value (e.g., 255) which will say this is a ref. Should probably have a function (is_ref()) to abstract this check.

int8_t pad;
} external;
struct internal_type {
Expand Down Expand Up @@ -106,6 +107,7 @@ public:
struct initialized_later {};

basic_sstring() noexcept {
u.external.is_ref = false;
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@nyh nyh Dec 10, 2020 •
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No, "u" is a union, you need to set either external or internal, you can't set both... In this constructor, the string is internal, so you musn't set external. The only byte common to both union members is the last one (size or pad). In fact, the sstring code would have been better and clearer if this byte was outside the union.

u.internal.size = 0;
if (NulTerminate) {
u.internal.str[0] = '\0';
Expand All @@ -115,13 +117,19 @@ public:
if (x.is_internal()) {
u.internal = x.u.internal;
} else {
u.external.is_ref = x.u.external.is_ref;
u.internal.size = -1;
u.external.str = reinterpret_cast<char_type*>(std::malloc(x.u.external.size + padding()));
if (!u.external.str) {
internal::throw_bad_alloc();
if(x.u.external.is_ref) {
u.external.str = x.u.external.str;
u.external.size = x.u.external.size;
} else {
u.external.str = reinterpret_cast<char_type*>(std::malloc(x.u.external.size + padding()));
if (!u.external.str) {
internal::throw_bad_alloc();
}
std::copy(x.u.external.str, x.u.external.str + x.u.external.size + padding(), u.external.str);
u.external.size = x.u.external.size;
}
std::copy(x.u.external.str, x.u.external.str + x.u.external.size + padding(), u.external.str);
u.external.size = x.u.external.size;
}
}
basic_sstring(basic_sstring&& x) noexcept {
Expand All @@ -145,6 +153,7 @@ public:
}
u.internal.size = size;
} else {
u.external.is_ref = false;
u.internal.size = -1;
u.external.str = reinterpret_cast<char_type*>(std::malloc(size + padding()));
if (!u.external.str) {
Expand All @@ -156,7 +165,14 @@ public:
}
}
}
basic_sstring(const char_type* x, size_t size) {
basic_sstring(const char_type* x, size_t size, bool is_ref = false) {
u.external.is_ref = is_ref;
if(is_ref) {
u.internal.size = -1;
u.external.str = (char*)x;
u.external.size = size;
return;
}
if (size_type(size) != size) {
internal::throw_sstring_overflow();
}
Expand All @@ -181,6 +197,7 @@ public:
}

basic_sstring(size_t size, char_type x) : basic_sstring(initialized_later(), size) {
u.external.is_ref = false;
memset(begin(), x, size);
}

Expand All @@ -199,11 +216,18 @@ public:
: basic_sstring(v.data(), v.size()) {
}
~basic_sstring() noexcept {
if (is_external()) {
if (is_external() && !u.external.is_ref) {
std::free(u.external.str);
}
}
basic_sstring& operator=(const basic_sstring& x) {
if (x.is_external() && x.u.external.is_ref) {
u.external.is_ref = x.u.external.is_ref;
u.internal.size = -1;
u.external.str = x.u.external.str;
u.external.size = x.u.external.size;
return *this;
}
basic_sstring tmp(x);
swap(tmp);
return *this;
Expand Down Expand Up @@ -303,6 +327,7 @@ public:
* @param c if n greater than current size character to fill newly allocated space with.
*/
void resize(size_t n, const char_type c = '\0') {
if(u.external.is_ref) return;
if (n > size()) {
*this += basic_sstring(n - size(), c);
} else if (n < size()) {
Expand Down Expand Up @@ -448,7 +473,7 @@ public:
// Deprecated March 2020.
[[deprecated("Use = {}")]]
void reset() noexcept {
if (is_external()) {
if (is_external() && !u.external.is_ref) {
std::free(u.external.str);
}
u.internal.size = 0;
Expand All @@ -462,6 +487,9 @@ public:
auto size = u.external.size;
u.external.str = nullptr;
u.external.size = 0;
if(u.external.is_ref) {
return temporary_buffer<char_type>(size);
}
return temporary_buffer<char_type>(ptr, size, make_free_deleter(ptr));
} else {
auto buf = temporary_buffer<char_type>(u.internal.size);
Expand Down