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author | wm4 <wm4@nowhere> | 2020-05-01 11:38:15 +0200 |
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committer | wm4 <wm4@nowhere> | 2020-05-01 11:38:15 +0200 |
commit | 994ccaea733db1c6be1d1798c4a60557d6ed226c (patch) | |
tree | f121d4ebc7542c8cd06adc7e430d43b0b854aad6 /ta/ta_utils.c | |
parent | 92db8731dd5ef700c7a7b96cf5f2f5aebc6d3d88 (diff) | |
download | mpv-rc.tar.bz2 mpv-rc.tar.xz |
ta: add refcount wrapperrc
Diffstat (limited to 'ta/ta_utils.c')
-rw-r--r-- | ta/ta_utils.c | 114 |
1 files changed, 114 insertions, 0 deletions
diff --git a/ta/ta_utils.c b/ta/ta_utils.c index 62469686db..ecba307a7a 100644 --- a/ta/ta_utils.c +++ b/ta/ta_utils.c @@ -17,6 +17,8 @@ #include <string.h> #include <stdio.h> #include <assert.h> + +#include "osdep/atomic.h" #include "osdep/strnlen.h" #define TA_NO_WRAPPERS @@ -313,3 +315,115 @@ char *ta_xstrndup(void *ta_parent, const char *str, size_t n) ta_oom_b(res || !str); return res; } + +struct ta_refcount { + atomic_ulong count; + void *child; + void (*on_free)(void *ctx, void *ta_child); + void *on_free_ctx; +}; + +// Allocate a refcount helper. The ta_child parameter is automatically freed +// with ta_free(). The returned object has a refcount of 1. Once the refcount +// reaches 0, ta_free(ta_child) is called. +// +// If on_free() is not NULL, then instead of ta_free(), on_free() is called with +// the parameters of the same named as passed to this function. +// +// The ta_child pointer must not be NULL, and must not have a parent allocation. +// Neither make any sense for this use-case, and could be hint for serious bugs +// in the caller, so assert()s check for this. +// +// The return value is not a ta allocation. You use the refcount functions to +// manage it. It is recommended to use ta_alloc_auto_unref(). +// +// Note: normally you use the ta_refcount_alloc() macro, which lacks the loc +// parameter. +struct ta_refcount *ta_refcount_alloc_(const char *loc, void *ta_child, + void (*on_free)(void *ctx, void *ta_child), + void *free_ctx) +{ + assert(ta_child && !ta_get_parent(ta_child)); + + struct ta_refcount *rc = ta_new_ptrtype(NULL, rc); + if (!rc) + return NULL; + + ta_dbg_set_loc(rc, loc); + *rc = (struct ta_refcount){ + .count = ATOMIC_VAR_INIT(1), + .child = ta_child, + .on_free = on_free, + .on_free_ctx = free_ctx, + }; + + return rc + 1; // "obfuscate" the pointer +} + +void ta_refcount_add(struct ta_refcount *rc) +{ + assert(rc); + rc -= 1; + + unsigned long c = atomic_fetch_add(&rc->count, 1); + assert(c > 0); // not allowed: refcount was 0, you can't "revive" it +} + +void ta_refcount_dec(struct ta_refcount *rc) +{ + assert(rc); + rc -= 1; + + unsigned long c = atomic_fetch_add(&rc->count, -1); + assert(c != 0); // not allowed: refcount was 0 + if (!c) { + if (rc->on_free) { + rc->on_free(rc->on_free_ctx, rc->child); + } else { + ta_free(rc->child); + } + ta_free(rc); + } +} + +// Return whether the refcount is 1. Note that if the result is false, it could +// become true any time in the general case, since other threads may be changing +// the refcount. But if true is returned, it means you are the only owner of the +// refcounted object. (If you are not an owner, it's UB to call this function.) +bool ta_refcount_is_1(struct ta_refcount *rc) +{ + assert(rc); + rc -= 1; + + return atomic_load(&rc->count) == 1; +} + +struct ta_refuser { + struct ta_refcount *rc; +}; + +static void autofree_dtor(void *p) +{ + struct ta_refuser *ru = p; + + ta_refcount_dec(ru->rc); +} + +// Refcount user helper. This is a ta allocation which on creation increments +// the refcount, and decrements it when it is free'd. +// +// The user must not access the contents of the allocation or resize it. Calling +// ta_set_destructor() is not allowed. But you can freely reparent it or add +// child allocation. ta_free_children() is also allowed and does not affect the +// refcount. +struct ta_refuser *ta_alloc_auto_ref(void *ta_parent, struct ta_refcount *rc) +{ + struct ta_refuser *ru = ta_new(ta_parent, struct ta_refuser); + if (!ru) + return NULL; + + ta_set_destructor(ru, autofree_dtor); + ru->rc = rc; + ta_refcount_add(ru->rc); + return ru; +} |