Delaying destructors and GC

Description

Due to destructors and the cycle collector, zval_ptr_dtor() may have more effects than just freeing the given zval. This is the cause of bugs and workarounds.

These bugs and workarounds could be avoided by delaying destructors and GC runs until a safepoint is reached. If we use vm interrupts as safepoints, this would delay destructors until the next branch/loop or function call (this should be defined more precisely), which seems reasonable.

I'm creating this ticket to aggregate issues that would not exist with delayed destructors and GC runs:

• 3d2b1753393b
• 6f38acfaf906
• https://bugs.php.net/bug.php?id=71020
• https://bugs.php.net/bug.php?id=73423
• https://github.com/php/php-src/issues/10168
• https://github.com/php/php-src/issues/13612
• https://github.com/php/php-src/issues/16464
• https://github.com/php/php-src/issues/16478
• https://github.com/php/php-src/issues/16479
• https://github.com/php/php-src/issues/16646
• https://github.com/php/php-src/issues/17162
• https://github.com/php/php-src/issues/18209
• https://github.com/php/php-src/issues/19999
• https://github.com/php/php-src/issues/20405
• https://github.com/php/php-src/issues/20477
• https://github.com/php/php-src/issues/20657
• https://github.com/php/php-src/issues/21824
• https://github.com/php/php-src/issues/22061
• https://github.com/php/php-src/issues/22062

https://github.com/php/php-src/pull/19787 delays GC runs, but not destructors.

zval_ptr_dtor() と VM-interrupt/safepoint の議論から始め、次に GC の実行は遅延させるがデストラクタは遅延させない pull request 19787 と比較してください。完了とするには、定義された safepoint ポリシーと、issue に列挙された集約されたケースに対処する完全な実装が必要です。