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When using PHP to develop extensions or write high-performance PHP applications, many developers will encounter thread safety (TS) problems. Especially when PHP is run in threaded (such as PHP ZTS under Windows or worker mode in certain special environments such as Apache mod_php), if the init function is written improperly, it may cause thread safety problems, resulting in data confusion, crashes and even security vulnerabilities.
This article will explain in detail how to identify these problems and how to safely write init functions in PHP to ensure that they run correctly in a multi-threaded environment.
Thread safety refers to: when multiple threads access the same piece of code at the same time, the code can ensure the correctness and consistency of data, and will not cause race conditions or data corruption due to concurrency.
In PHP, most scripts run in single threads (such as FPM mode), but if you write PHP extensions or work in ZTS mode, static variables, global variables, shared resources, etc. will cause thread safety issues.
A typical init function might contain:
Static variable initialization
Creation of singleton objects
Initialization of connection pools and cache pools
Allocation of global resources
For example:
function init() {
static $initialized = false;
if (!$initialized) {
// Execute one-time initialization logic
setup_connection('https://gitbox.net/api/setup');
$initialized = true;
}
}
In a single thread, there is no problem with such code. However, under multi-threading, if multiple threads enter init at the same time, $initialized may be found to be false , thereby performing the initialization repeatedly, and even destroying shared resources.
The most direct way is to lock the outer layer of the initialization logic to ensure that only one thread can execute at the same time.
$lock = fopen('/tmp/init.lock', 'c');
function init() {
global $lock;
static $initialized = false;
if (!$initialized) {
flock($lock, LOCK_EX);
if (!$initialized) {
setup_connection('https://gitbox.net/api/setup');
$initialized = true;
}
flock($lock, LOCK_UN);
}
}
This method is simple and effective, but pay attention to the overhead of file locks and possible blockage.
If you are writing PHP extensions, PHP provides a TSRM (Thread Safe Resource Manager) mechanism that allows you to use TSRMLS variables to store data separately in each thread, avoiding sharing global variables.
For example:
#ifdef ZTS
void ***tsrm_ls = NULL;
#endif
PHP_FUNCTION(init) {
// use TSRMLS Get local thread storage
}
However, this belongs to the C-level implementation and requires understanding of the PHP kernel.
If possible, try to keep the init function free of side effects, i.e.:
Do not modify global or static variables;
Not relying on shared resources;
Each thread initializes its own context independently.
Although this design requires reconstruction, it is the most fundamental solution.
To solve the thread safety problem of init functions in PHP, you need:
? Identify static variables and global states;
? Use lock mechanism to protect key segments;
? Use TSRM for thread isolation in extensions;
? Try to avoid sharing state when designing.
This will ensure that your code is stable and reliable in a multi-threaded environment without any obscure bugs.
If you have specific extension development requirements or thread safety questions, you can visit https://gitbox.net/php-ts-guide to view a more detailed development manual.
