What is the difference between the two versions of PHP5 Non-thread-safe and Thread-safe?

Non-thread-safe Non-threading Security and IIS Collocation environment
Thread-safe  Thread  -safe environment with Apache

For the user, this PHP debug pack is meaningless.

Not for PHP developers to debug PHP code.

is for C + + programmers to develop or modify PHP extensions.

For the user, this PHP debug pack is meaningless
This package is provided to developers, if you will C + + then you should know that the C + + project generated files are saved in the debug directory

Although PHP is open source, but his core code is not open source, but in the form of LIB to provide developers

Of course not for PHP developers to debug PHP code
is for C + + programmers to develop or modify the PHP extension

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What is the difference between the two versions of PHP5 Non-thread-safe and Thread-safe?