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chore(functions): add lazy global var details #1302

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chore(functions): add lazy global var details #1302

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7 changes: 7 additions & 0 deletions functions/tips_scopes/index.php
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@ function _lightComputation(): int
}

// [START functions_tips_scopes]
// [START functions_tips_lazy_globals]
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This sample is shown in the docs in adjacent sections of the same doc, I don't think it makes a lot of sense to reuse across both. I think either we don't need this snippet or it needs to be separate for clarity.


use Psr\Http\Message\ServerRequestInterface;

Expand All @@ -41,6 +42,11 @@ function scopeDemo(ServerRequestInterface $request): string
$cachePath = sys_get_temp_dir() . '/cached_value.txt';

$response = '';

// Because the PHP runtime does NOT cache global variables between
// invocations, there is no benefit to "greedily" initializing them
// in global scope. Thus, we ALWAYS initialize them "lazily" within
// the function itself
Comment on lines +47 to +49
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@grayside grayside Mar 12, 2021 •
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This guidance isn't quite right. The problem is not the lack of persisting global variables in this case, if that were the case the code below would work. The problem is that when the container starts, PHP code doesn't execute until a request comes in that loads the file.

Moving forward, we should keep in mind the larger goal of these samples: it's not about working with global variables, it's about using the language facility available to balance the amount of work done on cold start vs. function execution.

Future: We should research https://www.php.net/manual/en/opcache.preloading.php as a suggestion of this sample or a default configuration of the FF. In theory, if we set preload to the index.php file, we do get globals that can persist across requests.

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#1304 addresses preloading. @grayside we should discuss there how we want to approach this.

(If we do decide to use preloading, then we can incorporate it into this sample.)

if (file_exists($cachePath)) {
// Read cached value from file
$response .= "Reading cached value." . PHP_EOL;
Expand All @@ -61,4 +67,5 @@ function scopeDemo(ServerRequestInterface $request): string
return $response;
}

// [END functions_tips_lazy_globals]
// [END functions_tips_scopes]