iOS – header map加快编译速度（一）

本文介绍: h map – header m a p 描述头文件映射关系.m 文件 -&g t; 最终app 的简单过程主要是两部分这两个阶段都需要时间，要考虑如何加快编译速度，首先得选择在以上哪个阶段处理，选择的标准就是看哪个阶段的耗时更长，处理才变得更有意义编译消耗时间编译阶段消耗时长与链接消耗时间时间差一个数量级，所以处理编译阶段时间优化更有效如果头文件目录很多，意味着耗时进一步增加针对于编译.o 优化的几种方式组件二进制化提前编译二进制库文件(打包静态库 dylibs framework)…

h m a p – header m a p 描述头文件映射关系

.m文件 -&g t; 最终app 的简单过程主要是两部分

这两个阶段都需要时间，要考虑如何加快编译速度，首先得选择在以上哪个阶段处理，选择的标准就是看哪个阶段的耗时更长，处理才变得更有意义

编译消耗时间 167毫秒，链接消耗时间

时间差一个数量级，所以处理编译阶段时间优化更有效

如果头文件目录很多，意味着耗时进一步增加

framework module Masonry {
  umbrella header "Masonry-umbrella.h"

  export *
  module * { export * }
}

void read_hmap(void) {
    // test_hmap/Test111-all-non-framework-target-headers.hmap
    // test_hmap/Test111-all-target-headers.hmap
    // test_hmap/Test111-own-target-headers.hmap
    // test_hmap/Test111-project-headers.hmap
    // test_hmap/IFLTestSymbol-all-target-headers.hmap
    // test_hmap/IFLTestSymbol-generated-files.hmap
    // test_hmap/IFLTestSymbol-own-target-headers.hmap
    // test_hmap/IFLTestSymbol-project-headers.hmap
//    char *path = "/Users/erlich/Developer/workspace/ios/test/test_symbol/Test111/HMap/Test111.build/Debug-macosx/Test111.build/Test111-project-headers.hmap";
    char *path = "/Users/erlich/Developer/workspace/ios/test/test_symbol/Test111/Test111/test_hmap/Test111-project-headers.hmap";
    int file = open(path, O_RDONLY|O_CLOEXEC);
    if (file < 0) {
        printf("cannot open file %s", path);
        return;
    }
    struct HMapHeader *header = malloc(100 * sizeof(struct HMapHeader));
    ssize_t headerRead = read(file, header, 100 * sizeof(struct HMapHeader));
    if (headerRead < 0 || (size_t)headerRead < sizeof(struct HMapHeader)) {
        printf("read %s fail", path);
        close(file);
        return;
    }
    close(file);
    
    // Sniff it to see if it's a headermap by checking the magic number and version.
    bool needsByteSwap = false;
    if (header->Magic == ByteSwap_32(HMAP_HeaderMagicNumber) &amp;&amp; header->Version == ByteSwap_32(HMAP_HeaderVersion)) {
        // 高低位变换
        needsByteSwap = true;
    }
    
    uint32_t NumBuckets = needsByteSwap ? ByteSwap_32(header->NumBuckets) : header->NumBuckets;
    uint32_t StringsOffset = needsByteSwap ? ByteSwap_32(header->StringsOffset) : header->StringsOffset;
    
    const void *raw = (const void *)header;
    
    // HMapBucket 数组
    const void *buckets = raw + 24;
    // 长字符串
    const void *string_table = raw + 24 + 8 + header->StringsOffset;

    printf("buckets 初始化了: %inn", NumBuckets);
//    printf("长字符串：%snn", string_table);
    
    int mBucketsCount = 0;
    for (uint32_t i = 0; i < NumBuckets; i++) {
        struct HMapBucket *bucket = (struct HMapBucket *)(buckets + i * sizeof(struct HMapBucket));
        bucket->Key = needsByteSwap ? ByteSwap_32(bucket->Key) : bucket->Key;
        bucket->Prefix = needsByteSwap ? ByteSwap_32(bucket->Prefix) : bucket->Prefix;
        bucket->Suffix = needsByteSwap ? ByteSwap_32(bucket->Suffix) : bucket->Suffix;
        
        if (bucket->Key == 0 &amp;&amp; bucket->Prefix == 0 &amp;&amp; bucket->Suffix == 0) {
            continue;
        }
        mBucketsCount++;
        const char *key = string_table + bucket->Key;
        const char *prefix = string_table + bucket->Prefix;
        const char *suffix = string_table + bucket->Suffix;

        printf("key: %s, offset: %i nprefix: %s, offset: %i, nsuffix: %s, offset: %inn", key, bucket->Key, prefix, bucket->Prefix, suffix, bucket->Suffix);
    }
    
    printf("buckets 初始化了%i个，实际使用了%i个nn", NumBuckets, mBucketsCount);
    
    free(header);
}