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.

从 zval_ptr_dtor() 和 VM-interrupt/safepoint 讨论开始，然后比较 pull request 19787；该 pull request 会延迟 GC 运行，但不会延迟析构函数。要完成这项工作，需要定义明确的 safepoint 策略，并完成能够处理 issue 中列出的汇总案例的实现。