Native Memory Allocation and Ownership
When working with PHP FFI, you interact with native memory directly. This means you must be aware of how memory is allocated, who is responsible for freeing it, and the consequences of neglecting explicit memory management. The FFI::new() function is central to this process. When you call FFI::new(), PHP allocates a block of native memory for the specified C type. This memory is managed by PHP and will be automatically freed when the corresponding PHP object is destroyed—typically when it goes out of scope or is unset. However, if you pass this memory to native C functions that expect to take ownership, or if you use FFI::memcpy() to copy data into other native buffers, you may need to manage memory manually.
There is an important distinction between PHP-managed and C-managed memory:
- Memory allocated with
FFI::new()is managed by PHP; - Memory returned from C functions (for example, via
malloc()in C) is not; - In such cases, you are responsible for freeing the memory using the appropriate C function, such as
free(), via FFI; - Failing to do so can result in memory leaks, particularly in long-running or daemonized PHP processes.
When using FFI::memcpy(), you can copy data between PHP-managed and C-managed memory. However, the responsibility for freeing memory always follows the allocation: PHP frees what it allocates with FFI::new(), and you must free what C allocates. Always be conscious of this boundary to avoid resource leaks.
ffi_struct_example.php
1234567891011121314151617181920212223<?php // Load FFI and define a simple struct $ffi = FFI::cdef(" typedef struct { int x; double y; } Point; "); // Allocate a new Point struct in native memory (PHP-managed) $point = $ffi->new("Point"); // Modify struct fields $point->x = 42; $point->y = 3.14; // Output the struct fields echo "x: " . $point->x . "\n"; echo "y: " . $point->y . "\n"; // Explicitly free the memory (optional, but can be useful in long-running scripts) FFI::free($point); ?>
A common mistake when working with FFI and native memory in PHP is neglecting to free memory that is not PHP-managed. If you allocate memory in C (for instance, by calling a native malloc() through FFI) and do not call the corresponding free(), you will create a memory leak. This is especially problematic in long-running PHP processes, such as workers or daemons, where even small leaks can accumulate and exhaust system resources over time. Always track which side—PHP or C—owns each memory block, and ensure it is freed appropriately.
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When working with PHP FFI, you interact with native memory directly. This means you must be aware of how memory is allocated, who is responsible for freeing it, and the consequences of neglecting explicit memory management. The FFI::new() function is central to this process. When you call FFI::new(), PHP allocates a block of native memory for the specified C type. This memory is managed by PHP and will be automatically freed when the corresponding PHP object is destroyed—typically when it goes out of scope or is unset. However, if you pass this memory to native C functions that expect to take ownership, or if you use FFI::memcpy() to copy data into other native buffers, you may need to manage memory manually.
There is an important distinction between PHP-managed and C-managed memory:
- Memory allocated with
FFI::new()is managed by PHP; - Memory returned from C functions (for example, via
malloc()in C) is not; - In such cases, you are responsible for freeing the memory using the appropriate C function, such as
free(), via FFI; - Failing to do so can result in memory leaks, particularly in long-running or daemonized PHP processes.
When using FFI::memcpy(), you can copy data between PHP-managed and C-managed memory. However, the responsibility for freeing memory always follows the allocation: PHP frees what it allocates with FFI::new(), and you must free what C allocates. Always be conscious of this boundary to avoid resource leaks.
ffi_struct_example.php
1234567891011121314151617181920212223<?php // Load FFI and define a simple struct $ffi = FFI::cdef(" typedef struct { int x; double y; } Point; "); // Allocate a new Point struct in native memory (PHP-managed) $point = $ffi->new("Point"); // Modify struct fields $point->x = 42; $point->y = 3.14; // Output the struct fields echo "x: " . $point->x . "\n"; echo "y: " . $point->y . "\n"; // Explicitly free the memory (optional, but can be useful in long-running scripts) FFI::free($point); ?>
A common mistake when working with FFI and native memory in PHP is neglecting to free memory that is not PHP-managed. If you allocate memory in C (for instance, by calling a native malloc() through FFI) and do not call the corresponding free(), you will create a memory leak. This is especially problematic in long-running PHP processes, such as workers or daemons, where even small leaks can accumulate and exhaust system resources over time. Always track which side—PHP or C—owns each memory block, and ensure it is freed appropriately.
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