JavaScript-1.5 Reference
JS_GC Function
Summary
Performs garbage collection in the JS memory pool.
Syntax
void JS_GC(JSContext *cx);
Description
JS_GC performs garbage collection, if necessary, of JS objects, doubles, and
strings that are no longer needed by a script executing in a specified
JSContext, cx. Garbage collection frees space in the memory pool so that it
can be reused by the JS engine.
When you use JS_malloc and JS_realloc to allocate memory for executable
script contexts, these routines automatically invoke the garbage collection
routine.
When your scripts create many objects, you may want to call JS_GC directly
in your code, particularly when request ends or a script terminates. To run
garbage collection only when a certain amount of memory has been allocated,
you can call JS_MaybeGC instead of JS_GC.
JS_malloc Function
Summary
Allocates a region of memory for use.
Syntax
void * JS_malloc(JSContext *cx, size_t nbytes);
Name Type Description
cx JSContext * Pointer to a JS context from which to derive runtime
information.
nbytes size_t Amount of space, in bytes, to allocate.
Description
JS_malloc allocates a region of memory nbytes in size. If the allocation is
successful, JS_malloc returns a pointer to the beginning of the region.
If the memory cannot be allocated, JS_malloc passes cx to
JS_ReportOutOfMemory to report the error, and returns a null pointer.
As with a standard C call to malloc, the region of memory allocated by this
call is uninitialized and should be assumed to contain meaningless
information.
Notes
Currently JS_malloc is a wrapper on the standard C malloc call. Do not make
assumptions based on this underlying reliance. Future versions of JS_malloc
may be implemented in a different manner.
JS_realloc Function
Summary
Reallocates a region of memory.
Syntax
void * JS_realloc(JSContext *cx, void *p, size_t nbytes);
Name Type Description
cx JSContext * Pointer to a JS context from which to derive runtime
information.
p void * Pointer to the previously allocated memory
nbytes size_t Amount of space, in bytes, to reallocate.
Description
JS_realloc reallocates a region of memory, while preserving its contents.
Typically you call JS_realloc because you need to allocate more memory than
orginally allocated with a call to JS_malloc, but it can also be called to
decrease the amount of allocated memory, and even to deallocate the memory
region entirely. p is a pointer to the previously allocated memory region,
and nbytes is the size, in bytes, of the region to allocate.
Notes
Currently JS_realloc is a wrapper on the standard C realloc call. Do not
make assumptions based on this underlying reliance. Future versions of
JS_realloc may be implemented in a different manner.
If p is null, then JS_realloc behaves like JS_malloc. If p is not null, and
nbytes is 0, JS_realloc returns null and the region is deallocated. As with
JS_malloc, new space is not initialized and should be regarded to contain
meaningless information.
If a reallocation request fails, JS_realloc passes cx to
JS_ReportOutOfMemory to report the error.
Whenever the pointer returned by JS_realloc differs from p, the old region
of memory is deallocated and should not be used.
JS_MaybeGC Function
Summary
Invokes conditional garbage collection on the JS memory pool.
Syntax
void JS_MaybeGC(JSContext *cx);
Description
JS_MaybeGC performs a conditional garbage collection of JS objects, doubles,
and strings that are no longer needed by a script executing in a specified
JSContext, cx. This function checks that about 75% of available space has
already been allocated to objects before peforming garbage collection. To
force garbage collection regardless of the amount of allocated space, call
JS_GC instead of JS_MaybeGC.
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