/*
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* Copyright (c) 2014, Facebook, Inc.
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* All rights reserved.
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*
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* This source code is licensed under the BSD-style license found in the
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* LICENSE file in the root directory of this source tree. An additional grant
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* of patent rights can be found in the PATENTS file in the same directory.
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*
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*/
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#import "OSSExecutor.h"
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#import <pthread.h>
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NS_ASSUME_NONNULL_BEGIN
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/*!
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Get the remaining stack-size of the current thread.
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@param totalSize The total stack size of the current thread.
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@return The remaining size, in bytes, available to the current thread.
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@note This function cannot be inlined, as otherwise the internal implementation could fail to report the proper
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remaining stack space.
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*/
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__attribute__((noinline)) static size_t remaining_stack_size(size_t *restrict totalSize) {
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pthread_t currentThread = pthread_self();
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// NOTE: We must store stack pointers as uint8_t so that the pointer math is well-defined
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uint8_t *endStack = pthread_get_stackaddr_np(currentThread);
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*totalSize = pthread_get_stacksize_np(currentThread);
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// NOTE: If the function is inlined, this value could be incorrect
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uint8_t *frameAddr = __builtin_frame_address(0);
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return (*totalSize) - (endStack - frameAddr);
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}
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@interface OSSExecutor ()
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@property (nonatomic, copy) void(^block)(void(^block)(void));
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@end
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@implementation OSSExecutor
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#pragma mark - Executor methods
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+ (instancetype)defaultExecutor {
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static OSSExecutor *defaultExecutor = NULL;
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static dispatch_once_t onceToken;
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dispatch_once(&onceToken, ^{
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defaultExecutor = [self executorWithBlock:^void(void(^block)(void)) {
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// We prefer to run everything possible immediately, so that there is callstack information
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// when debugging. However, we don't want the stack to get too deep, so if the remaining stack space
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// is less than 10% of the total space, we dispatch to another GCD queue.
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size_t totalStackSize = 0;
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size_t remainingStackSize = remaining_stack_size(&totalStackSize);
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if (remainingStackSize < (totalStackSize / 10)) {
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dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), block);
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} else {
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@autoreleasepool {
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block();
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}
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}
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}];
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});
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return defaultExecutor;
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}
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+ (instancetype)immediateExecutor {
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static OSSExecutor *immediateExecutor = NULL;
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static dispatch_once_t onceToken;
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dispatch_once(&onceToken, ^{
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immediateExecutor = [self executorWithBlock:^void(void(^block)(void)) {
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block();
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}];
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});
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return immediateExecutor;
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}
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+ (instancetype)mainThreadExecutor {
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static OSSExecutor *mainThreadExecutor = NULL;
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static dispatch_once_t onceToken;
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dispatch_once(&onceToken, ^{
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mainThreadExecutor = [self executorWithBlock:^void(void(^block)(void)) {
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if (![NSThread isMainThread]) {
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dispatch_async(dispatch_get_main_queue(), block);
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} else {
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@autoreleasepool {
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block();
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}
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}
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}];
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});
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return mainThreadExecutor;
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}
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+ (instancetype)executorWithBlock:(void(^)(void(^block)(void)))block {
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return [[self alloc] initWithBlock:block];
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}
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+ (instancetype)executorWithDispatchQueue:(dispatch_queue_t)queue {
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return [self executorWithBlock:^void(void(^block)(void)) {
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dispatch_async(queue, block);
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}];
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}
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+ (instancetype)executorWithOperationQueue:(NSOperationQueue *)queue {
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return [self executorWithBlock:^void(void(^block)(void)) {
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[queue addOperation:[NSBlockOperation blockOperationWithBlock:block]];
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}];
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}
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#pragma mark - Initializer
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- (instancetype)initWithBlock:(void(^)(void(^block)(void)))block {
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self = [super init];
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if (!self) return self;
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_block = block;
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return self;
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}
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#pragma mark - Execution
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- (void)execute:(void(^)(void))block {
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self.block(block);
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}
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@end
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NS_ASSUME_NONNULL_END
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