Unique dating site usernames
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Prefix can be useful, for instance, if you generate identifiers simultaneously on several hosts that might happen to generate the identifier at the same microsecond.So we can include the hostname / servername in the id.
Although it could be just my bad programming, I found exactly 1 collission while debugging my code.
One simple solution is to compare the latest value returned with the previous result, and keep calling in a loop until the new value is different, if you don't mind this call causing a delay of 1 microsecond per call when necessary.
The php5-uuid functions could definitely use some documentation to clarify how they should be used, but here's what I've gleaned by examining the OSSP source code (found here:
The uuid_make() function takes two arguments when generating v1 or v4, but four arguments are required when generating v3 or v5.
The first two arguments have been demonstrated below and are straightforward, so I'll skip to the as-yet non-described arguments.
The third argument to uuid_make() is: $namespace - this is a secondary resource created with uuid_create(); it is apparently used to generate an internal UUID, which is used as the namespace of the output UUIDThe fourth argument to uuid_make() is: $url - this is the value that is to be hashed (MD5 for v3, SHA-1 for v5); it may be any string or even null Here's a simple class illustrating the proper usage (note that if php5-uuid is not installed on your system, each function call will just return false): And the output:microtime = 1306620716.0457V1 UUID: 7fddae8e-8977-11e0-bc11-003048c3b1f2V3 UUID of URL='abc': 522ec739-ca63-3ec5-b082-08ce08ad65e2V4 UUID: b3851ec7-4871-4527-92b5-ef5616bae1e6V5 UUID of URL=null: e129f27c-5103-5c5c-844b-cdf0a15e160d-------------------microtime = 1306620716.0465V1 UUID: 7fddb83e-8977-11e0-9e6e-003048c3b1f2V3 UUID of URL='abc': 522ec739-ca63-3ec5-b082-08ce08ad65e2V4 UUID: 7e78fe0d-59b8-4637-af7f-e88d221a7d1e V5 UUID of URL=null: e129f27c-5103-5c5c-844b-cdf0a15e160d-------------------microtime = 1306620716.0467V1 UUID: 7fddbfb4-8977-11e0-a2bc-003048c3b1f2V3 UUID of URL='abc': 522ec739-ca63-3ec5-b082-08ce08ad65e2V4 UUID: 12a940c7-0f3f-46a1-bb5f-bdd602e10654V5 UUID of URL=null: e129f27c-5103-5c5c-844b-cdf0a15e160d As you can see, the calls to v3() always return the same UUID because the same URL parameter, "abc", is always supplied.
The same goes for the v5() function which is always supplied a null URL.The v4() UUIDs are always entirely different because they are (pseudo)random.And the v1() calls are very similar but just slightly different because it's based on the computer's MAC address and the current time.Warning This function does not guarantee uniqueness of return value.Since most systems adjust system clock by NTP or like, system time is changed constantly.Therefore, it is possible that this function does not return unique ID for the process/thread.